Re: [PATCH 06/51] drm/i915/guc: Implement GuC context operations for new inteface

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On Mon, Jul 19, 2021 at 05:51:46PM -0700, Daniele Ceraolo Spurio wrote:
> 
> 
> On 7/16/2021 1:16 PM, Matthew Brost wrote:
> > Implement GuC context operations which includes GuC specific operations
> > alloc, pin, unpin, and destroy.
> > 
> > v2:
> >   (Daniel Vetter)
> >    - Use msleep_interruptible rather than cond_resched in busy loop
> >   (Michal)
> >    - Remove C++ style comment
> > 
> > Signed-off-by: John Harrison <John.C.Harrison@xxxxxxxxx>
> > Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
> > ---
> >   drivers/gpu/drm/i915/gt/intel_context.c       |   5 +
> >   drivers/gpu/drm/i915/gt/intel_context_types.h |  22 +-
> >   drivers/gpu/drm/i915/gt/intel_lrc_reg.h       |   1 -
> >   drivers/gpu/drm/i915/gt/uc/intel_guc.h        |  40 ++
> >   drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c     |   4 +
> >   .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 666 ++++++++++++++++--
> >   drivers/gpu/drm/i915/i915_reg.h               |   1 +
> >   drivers/gpu/drm/i915/i915_request.c           |   1 +
> >   8 files changed, 685 insertions(+), 55 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
> > index bd63813c8a80..32fd6647154b 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_context.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_context.c
> > @@ -384,6 +384,11 @@ intel_context_init(struct intel_context *ce, struct intel_engine_cs *engine)
> >   	mutex_init(&ce->pin_mutex);
> > +	spin_lock_init(&ce->guc_state.lock);
> > +
> > +	ce->guc_id = GUC_INVALID_LRC_ID;
> > +	INIT_LIST_HEAD(&ce->guc_id_link);
> > +
> >   	i915_active_init(&ce->active,
> >   			 __intel_context_active, __intel_context_retire, 0);
> >   }
> > diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h
> > index 6d99631d19b9..606c480aec26 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_context_types.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
> > @@ -96,6 +96,7 @@ struct intel_context {
> >   #define CONTEXT_BANNED			6
> >   #define CONTEXT_FORCE_SINGLE_SUBMISSION	7
> >   #define CONTEXT_NOPREEMPT		8
> > +#define CONTEXT_LRCA_DIRTY		9
> >   	struct {
> >   		u64 timeout_us;
> > @@ -138,14 +139,29 @@ struct intel_context {
> >   	u8 wa_bb_page; /* if set, page num reserved for context workarounds */
> > +	struct {
> > +		/** lock: protects everything in guc_state */
> > +		spinlock_t lock;
> > +		/**
> > +		 * sched_state: scheduling state of this context using GuC
> > +		 * submission
> > +		 */
> > +		u8 sched_state;
> > +	} guc_state;
> > +
> >   	/* GuC scheduling state flags that do not require a lock. */
> >   	atomic_t guc_sched_state_no_lock;
> > +	/* GuC LRC descriptor ID */
> > +	u16 guc_id;
> > +
> > +	/* GuC LRC descriptor reference count */
> > +	atomic_t guc_id_ref;
> > +
> >   	/*
> > -	 * GuC LRC descriptor ID - Not assigned in this patch but future patches
> > -	 * in the series will.
> > +	 * GuC ID link - in list when unpinned but guc_id still valid in GuC
> >   	 */
> > -	u16 guc_id;
> > +	struct list_head guc_id_link;
> >   };
> >   #endif /* __INTEL_CONTEXT_TYPES__ */
> > diff --git a/drivers/gpu/drm/i915/gt/intel_lrc_reg.h b/drivers/gpu/drm/i915/gt/intel_lrc_reg.h
> > index 41e5350a7a05..49d4857ad9b7 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_lrc_reg.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_lrc_reg.h
> > @@ -87,7 +87,6 @@
> >   #define GEN11_CSB_WRITE_PTR_MASK	(GEN11_CSB_PTR_MASK << 0)
> >   #define MAX_CONTEXT_HW_ID	(1 << 21) /* exclusive */
> > -#define MAX_GUC_CONTEXT_HW_ID	(1 << 20) /* exclusive */
> >   #define GEN11_MAX_CONTEXT_HW_ID	(1 << 11) /* exclusive */
> >   /* in Gen12 ID 0x7FF is reserved to indicate idle */
> >   #define GEN12_MAX_CONTEXT_HW_ID	(GEN11_MAX_CONTEXT_HW_ID - 1)
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> > index 8c7b92f699f1..30773cd699f5 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> > @@ -7,6 +7,7 @@
> >   #define _INTEL_GUC_H_
> >   #include <linux/xarray.h>
> > +#include <linux/delay.h>
> >   #include "intel_uncore.h"
> >   #include "intel_guc_fw.h"
> > @@ -44,6 +45,14 @@ struct intel_guc {
> >   		void (*disable)(struct intel_guc *guc);
> >   	} interrupts;
> > +	/*
> > +	 * contexts_lock protects the pool of free guc ids and a linked list of
> > +	 * guc ids available to be stolen
> > +	 */
> > +	spinlock_t contexts_lock;
> > +	struct ida guc_ids;
> > +	struct list_head guc_id_list;
> > +
> >   	bool submission_selected;
> >   	struct i915_vma *ads_vma;
> > @@ -101,6 +110,34 @@ intel_guc_send_and_receive(struct intel_guc *guc, const u32 *action, u32 len,
> >   				 response_buf, response_buf_size, 0);
> >   }
> > +static inline int intel_guc_send_busy_loop(struct intel_guc* guc,
> > +					   const u32 *action,
> > +					   u32 len,
> > +					   bool loop)
> > +{
> > +	int err;
> > +	unsigned int sleep_period_ms = 1;
> > +	bool not_atomic = !in_atomic() && !irqs_disabled();
> > +
> > +	/* No sleeping with spin locks, just busy loop */
> > +	might_sleep_if(loop && not_atomic);
> > +
> > +retry:
> > +	err = intel_guc_send_nb(guc, action, len);
> > +	if (unlikely(err == -EBUSY && loop)) {
> > +		if (likely(not_atomic)) {
> > +			if (msleep_interruptible(sleep_period_ms))
> > +				return -EINTR;
> > +			sleep_period_ms = sleep_period_ms << 1;
> > +		} else {
> > +			cpu_relax();
> 
> Potentially something we can change later, but if we're in atomic context we
> can't keep looping without a timeout while we get -EBUSY, we need to bail
> out early.
>

Eventually intel_guc_send_nb will pop with a different return code after
1 second I think if the GuC is hung.
 
> > +		}
> > +		goto retry;
> > +	}
> > +
> > +	return err;
> > +}
> > +
> >   static inline void intel_guc_to_host_event_handler(struct intel_guc *guc)
> >   {
> >   	intel_guc_ct_event_handler(&guc->ct);
> > @@ -202,6 +239,9 @@ static inline void intel_guc_disable_msg(struct intel_guc *guc, u32 mask)
> >   int intel_guc_reset_engine(struct intel_guc *guc,
> >   			   struct intel_engine_cs *engine);
> > +int intel_guc_deregister_done_process_msg(struct intel_guc *guc,
> > +					  const u32 *msg, u32 len);
> > +
> >   void intel_guc_load_status(struct intel_guc *guc, struct drm_printer *p);
> >   #endif
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> > index 83ec60ea3f89..28ff82c5be45 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> > @@ -928,6 +928,10 @@ static int ct_process_request(struct intel_guc_ct *ct, struct ct_incoming_msg *r
> >   	case INTEL_GUC_ACTION_DEFAULT:
> >   		ret = intel_guc_to_host_process_recv_msg(guc, payload, len);
> >   		break;
> > +	case INTEL_GUC_ACTION_DEREGISTER_CONTEXT_DONE:
> > +		ret = intel_guc_deregister_done_process_msg(guc, payload,
> > +							    len);
> > +		break;
> >   	default:
> >   		ret = -EOPNOTSUPP;
> >   		break;
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > index 53b4a5eb4a85..a47b3813b4d0 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > @@ -13,7 +13,9 @@
> >   #include "gt/intel_gt.h"
> >   #include "gt/intel_gt_irq.h"
> >   #include "gt/intel_gt_pm.h"
> > +#include "gt/intel_gt_requests.h"
> >   #include "gt/intel_lrc.h"
> > +#include "gt/intel_lrc_reg.h"
> >   #include "gt/intel_mocs.h"
> >   #include "gt/intel_ring.h"
> > @@ -85,6 +87,73 @@ static inline void clr_context_enabled(struct intel_context *ce)
> >   		   &ce->guc_sched_state_no_lock);
> >   }
> > +/*
> > + * Below is a set of functions which control the GuC scheduling state which
> > + * require a lock, aside from the special case where the functions are called
> > + * from guc_lrc_desc_pin(). In that case it isn't possible for any other code
> > + * path to be executing on the context.
> > + */
> 
> Is there a reason to avoid taking the lock in guc_lrc_desc_pin, even if it
> isn't strictly needed? I'd prefer to avoid the asymmetry in the locking

If this code is called from releasing a fence a circular dependency is
created. Once we move the DRM scheduler the locking becomes way easier
and we clean this up then. We already have task for locking clean up.

> scheme if possible, as that might case trouble if thing change in the
> future.

Again this is temporary code, so I think we can live with this until the
DRM scheduler lands.

> 
> > +#define SCHED_STATE_WAIT_FOR_DEREGISTER_TO_REGISTER	BIT(0)
> > +#define SCHED_STATE_DESTROYED				BIT(1)
> > +static inline void init_sched_state(struct intel_context *ce)
> > +{
> > +	/* Only should be called from guc_lrc_desc_pin() */
> > +	atomic_set(&ce->guc_sched_state_no_lock, 0);
> > +	ce->guc_state.sched_state = 0;
> > +}
> > +
> > +static inline bool
> > +context_wait_for_deregister_to_register(struct intel_context *ce)
> > +{
> > +	return (ce->guc_state.sched_state &
> > +		SCHED_STATE_WAIT_FOR_DEREGISTER_TO_REGISTER);
> 
> No need for (). Below as well.
> 

Yep.

> > +}
> > +
> > +static inline void
> > +set_context_wait_for_deregister_to_register(struct intel_context *ce)
> > +{
> > +	/* Only should be called from guc_lrc_desc_pin() */
> > +	ce->guc_state.sched_state |=
> > +		SCHED_STATE_WAIT_FOR_DEREGISTER_TO_REGISTER;
> > +}
> > +
> > +static inline void
> > +clr_context_wait_for_deregister_to_register(struct intel_context *ce)
> > +{
> > +	lockdep_assert_held(&ce->guc_state.lock);
> > +	ce->guc_state.sched_state =
> > +		(ce->guc_state.sched_state &
> > +		 ~SCHED_STATE_WAIT_FOR_DEREGISTER_TO_REGISTER);
> 
> nit: can also use
> 
> ce->guc_state.sched_state &=
> 	~SCHED_STATE_WAIT_FOR_DEREGISTER_TO_REGISTER
>

Yep.
 
> 
> > +}
> > +
> > +static inline bool
> > +context_destroyed(struct intel_context *ce)
> > +{
> > +	return (ce->guc_state.sched_state & SCHED_STATE_DESTROYED);
> > +}
> > +
> > +static inline void
> > +set_context_destroyed(struct intel_context *ce)
> > +{
> > +	lockdep_assert_held(&ce->guc_state.lock);
> > +	ce->guc_state.sched_state |= SCHED_STATE_DESTROYED;
> > +}
> > +
> > +static inline bool context_guc_id_invalid(struct intel_context *ce)
> > +{
> > +	return (ce->guc_id == GUC_INVALID_LRC_ID);
> > +}
> > +
> > +static inline void set_context_guc_id_invalid(struct intel_context *ce)
> > +{
> > +	ce->guc_id = GUC_INVALID_LRC_ID;
> > +}
> > +
> > +static inline struct intel_guc *ce_to_guc(struct intel_context *ce)
> > +{
> > +	return &ce->engine->gt->uc.guc;
> > +}
> > +
> >   static inline struct i915_priolist *to_priolist(struct rb_node *rb)
> >   {
> >   	return rb_entry(rb, struct i915_priolist, node);
> > @@ -155,6 +224,9 @@ static int guc_add_request(struct intel_guc *guc, struct i915_request *rq)
> >   	int len = 0;
> >   	bool enabled = context_enabled(ce);
> > +	GEM_BUG_ON(!atomic_read(&ce->guc_id_ref));
> > +	GEM_BUG_ON(context_guc_id_invalid(ce));
> > +
> >   	if (!enabled) {
> >   		action[len++] = INTEL_GUC_ACTION_SCHED_CONTEXT_MODE_SET;
> >   		action[len++] = ce->guc_id;
> > @@ -417,6 +489,10 @@ int intel_guc_submission_init(struct intel_guc *guc)
> >   	xa_init_flags(&guc->context_lookup, XA_FLAGS_LOCK_IRQ);
> > +	spin_lock_init(&guc->contexts_lock);
> > +	INIT_LIST_HEAD(&guc->guc_id_list);
> > +	ida_init(&guc->guc_ids);
> > +
> >   	return 0;
> >   }
> > @@ -429,9 +505,303 @@ void intel_guc_submission_fini(struct intel_guc *guc)
> >   	i915_sched_engine_put(guc->sched_engine);
> >   }
> > -static int guc_context_alloc(struct intel_context *ce)
> > +static inline void queue_request(struct i915_sched_engine *sched_engine,
> > +				 struct i915_request *rq,
> > +				 int prio)
> >   {
> > -	return lrc_alloc(ce, ce->engine);
> > +	GEM_BUG_ON(!list_empty(&rq->sched.link));
> > +	list_add_tail(&rq->sched.link,
> > +		      i915_sched_lookup_priolist(sched_engine, prio));
> > +	set_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);
> > +}
> > +
> > +static int guc_bypass_tasklet_submit(struct intel_guc *guc,
> > +				     struct i915_request *rq)
> > +{
> > +	int ret;
> > +
> > +	__i915_request_submit(rq);
> > +
> > +	trace_i915_request_in(rq, 0);
> > +
> > +	guc_set_lrc_tail(rq);
> > +	ret = guc_add_request(guc, rq);
> > +	if (ret == -EBUSY)
> > +		guc->stalled_request = rq;
> > +
> > +	return ret;
> > +}
> > +
> > +static void guc_submit_request(struct i915_request *rq)
> > +{
> > +	struct i915_sched_engine *sched_engine = rq->engine->sched_engine;
> > +	struct intel_guc *guc = &rq->engine->gt->uc.guc;
> > +	unsigned long flags;
> > +
> > +	/* Will be called from irq-context when using foreign fences. */
> > +	spin_lock_irqsave(&sched_engine->lock, flags);
> > +
> > +	if (guc->stalled_request || !i915_sched_engine_is_empty(sched_engine))
> > +		queue_request(sched_engine, rq, rq_prio(rq));
> > +	else if (guc_bypass_tasklet_submit(guc, rq) == -EBUSY)
> > +		tasklet_hi_schedule(&sched_engine->tasklet);
> > +
> > +	spin_unlock_irqrestore(&sched_engine->lock, flags);
> > +}
> > +
> > +#define GUC_ID_START	64	/* First 64 guc_ids reserved */
> > +static int new_guc_id(struct intel_guc *guc)
> > +{
> > +	return ida_simple_get(&guc->guc_ids, GUC_ID_START,
> > +			      GUC_MAX_LRC_DESCRIPTORS, GFP_KERNEL |
> > +			      __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
> > +}
> > +
> > +static void __release_guc_id(struct intel_guc *guc, struct intel_context *ce)
> > +{
> > +	if (!context_guc_id_invalid(ce)) {
> > +		ida_simple_remove(&guc->guc_ids, ce->guc_id);
> > +		reset_lrc_desc(guc, ce->guc_id);
> > +		set_context_guc_id_invalid(ce);
> > +	}
> > +	if (!list_empty(&ce->guc_id_link))
> > +		list_del_init(&ce->guc_id_link);
> > +}
> > +
> > +static void release_guc_id(struct intel_guc *guc, struct intel_context *ce)
> > +{
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&guc->contexts_lock, flags);
> > +	__release_guc_id(guc, ce);
> > +	spin_unlock_irqrestore(&guc->contexts_lock, flags);
> > +}
> > +
> > +static int steal_guc_id(struct intel_guc *guc)
> > +{
> > +	struct intel_context *ce;
> > +	int guc_id;
> > +
> > +	if (!list_empty(&guc->guc_id_list)) {
> > +		ce = list_first_entry(&guc->guc_id_list,
> > +				      struct intel_context,
> > +				      guc_id_link);
> > +
> > +		GEM_BUG_ON(atomic_read(&ce->guc_id_ref));
> > +		GEM_BUG_ON(context_guc_id_invalid(ce));
> > +
> > +		list_del_init(&ce->guc_id_link);
> > +		guc_id = ce->guc_id;
> > +		set_context_guc_id_invalid(ce);
> > +		return guc_id;
> > +	} else {
> > +		return -EAGAIN;
> > +	}
> > +}
> > +
> > +static int assign_guc_id(struct intel_guc *guc, u16 *out)
> > +{
> > +	int ret;
> > +
> > +	ret = new_guc_id(guc);
> > +	if (unlikely(ret < 0)) {
> > +		ret = steal_guc_id(guc);
> > +		if (ret < 0)
> > +			return ret;
> > +	}
> > +
> > +	*out = ret;
> > +	return 0;
> 
> Is it worth adding spinlock_held asserts for guc->contexts_lock in these ID
> functions? Doubles up as a documentation of what locking we expect.
> 

Never a bad idea to have asserts in the code. Will add.

> > +}
> > +
> > +#define PIN_GUC_ID_TRIES	4
> > +static int pin_guc_id(struct intel_guc *guc, struct intel_context *ce)
> > +{
> > +	int ret = 0;
> > +	unsigned long flags, tries = PIN_GUC_ID_TRIES;
> > +
> > +	GEM_BUG_ON(atomic_read(&ce->guc_id_ref));
> > +
> > +try_again:
> > +	spin_lock_irqsave(&guc->contexts_lock, flags);
> > +
> > +	if (context_guc_id_invalid(ce)) {
> > +		ret = assign_guc_id(guc, &ce->guc_id);
> > +		if (ret)
> > +			goto out_unlock;
> > +		ret = 1;	/* Indidcates newly assigned guc_id */
> > +	}
> > +	if (!list_empty(&ce->guc_id_link))
> > +		list_del_init(&ce->guc_id_link);
> > +	atomic_inc(&ce->guc_id_ref);
> > +
> > +out_unlock:
> > +	spin_unlock_irqrestore(&guc->contexts_lock, flags);
> > +
> > +	/*
> > +	 * -EAGAIN indicates no guc_ids are available, let's retire any
> > +	 * outstanding requests to see if that frees up a guc_id. If the first
> > +	 * retire didn't help, insert a sleep with the timeslice duration before
> > +	 * attempting to retire more requests. Double the sleep period each
> > +	 * subsequent pass before finally giving up. The sleep period has max of
> > +	 * 100ms and minimum of 1ms.
> > +	 */
> > +	if (ret == -EAGAIN && --tries) {
> > +		if (PIN_GUC_ID_TRIES - tries > 1) {
> > +			unsigned int timeslice_shifted =
> > +				ce->engine->props.timeslice_duration_ms <<
> > +				(PIN_GUC_ID_TRIES - tries - 2);
> > +			unsigned int max = min_t(unsigned int, 100,
> > +						 timeslice_shifted);
> > +
> > +			msleep(max_t(unsigned int, max, 1));
> > +		}
> > +		intel_gt_retire_requests(guc_to_gt(guc));
> > +		goto try_again;
> > +	}
> > +
> > +	return ret;
> > +}
> > +
> > +static void unpin_guc_id(struct intel_guc *guc, struct intel_context *ce)
> > +{
> > +	unsigned long flags;
> > +
> > +	GEM_BUG_ON(atomic_read(&ce->guc_id_ref) < 0);
> > +
> > +	spin_lock_irqsave(&guc->contexts_lock, flags);
> > +	if (!context_guc_id_invalid(ce) && list_empty(&ce->guc_id_link) &&
> > +	    !atomic_read(&ce->guc_id_ref))
> > +		list_add_tail(&ce->guc_id_link, &guc->guc_id_list);
> > +	spin_unlock_irqrestore(&guc->contexts_lock, flags);
> > +}
> > +
> > +static int __guc_action_register_context(struct intel_guc *guc,
> > +					 u32 guc_id,
> > +					 u32 offset)
> > +{
> > +	u32 action[] = {
> > +		INTEL_GUC_ACTION_REGISTER_CONTEXT,
> > +		guc_id,
> > +		offset,
> > +	};
> > +
> > +	return intel_guc_send_busy_loop(guc, action, ARRAY_SIZE(action), true);
> > +}
> > +
> > +static int register_context(struct intel_context *ce)
> > +{
> > +	struct intel_guc *guc = ce_to_guc(ce);
> > +	u32 offset = intel_guc_ggtt_offset(guc, guc->lrc_desc_pool) +
> > +		ce->guc_id * sizeof(struct guc_lrc_desc);
> > +
> > +	return __guc_action_register_context(guc, ce->guc_id, offset);
> > +}
> > +
> > +static int __guc_action_deregister_context(struct intel_guc *guc,
> > +					   u32 guc_id)
> > +{
> > +	u32 action[] = {
> > +		INTEL_GUC_ACTION_DEREGISTER_CONTEXT,
> > +		guc_id,
> > +	};
> > +
> > +	return intel_guc_send_busy_loop(guc, action, ARRAY_SIZE(action), true);
> > +}
> > +
> > +static int deregister_context(struct intel_context *ce, u32 guc_id)
> > +{
> > +	struct intel_guc *guc = ce_to_guc(ce);
> > +
> > +	return __guc_action_deregister_context(guc, guc_id);
> > +}
> > +
> > +static intel_engine_mask_t adjust_engine_mask(u8 class, intel_engine_mask_t mask)
> > +{
> > +	switch (class) {
> > +	case RENDER_CLASS:
> > +		return mask >> RCS0;
> > +	case VIDEO_ENHANCEMENT_CLASS:
> > +		return mask >> VECS0;
> > +	case VIDEO_DECODE_CLASS:
> > +		return mask >> VCS0;
> > +	case COPY_ENGINE_CLASS:
> > +		return mask >> BCS0;
> > +	default:
> > +		GEM_BUG_ON("Invalid Class");
> 
> we usually use MISSING_CASE for this type of errors.

As soon as start talking in logical space (series immediatly after this
gets merged) this function gets deleted but will fix.

> 
> > +		return 0;
> > +	}
> > +}
> > +
> > +static void guc_context_policy_init(struct intel_engine_cs *engine,
> > +				    struct guc_lrc_desc *desc)
> > +{
> > +	desc->policy_flags = 0;
> > +
> > +	desc->execution_quantum = CONTEXT_POLICY_DEFAULT_EXECUTION_QUANTUM_US;
> > +	desc->preemption_timeout = CONTEXT_POLICY_DEFAULT_PREEMPTION_TIME_US;
> > +}
> > +
> > +static int guc_lrc_desc_pin(struct intel_context *ce)
> > +{
> > +	struct intel_runtime_pm *runtime_pm =
> > +		&ce->engine->gt->i915->runtime_pm;
> 
> If you move this after the engine var below you can skip the ce->engine
> jump. Also, you can shorten the pointer chasing by using
> engine->uncore->rpm.
> 

Sure.

> > +	struct intel_engine_cs *engine = ce->engine;
> > +	struct intel_guc *guc = &engine->gt->uc.guc;
> > +	u32 desc_idx = ce->guc_id;
> > +	struct guc_lrc_desc *desc;
> > +	bool context_registered;
> > +	intel_wakeref_t wakeref;
> > +	int ret = 0;
> > +
> > +	GEM_BUG_ON(!engine->mask);
> > +
> > +	/*
> > +	 * Ensure LRC + CT vmas are is same region as write barrier is done
> > +	 * based on CT vma region.
> > +	 */
> > +	GEM_BUG_ON(i915_gem_object_is_lmem(guc->ct.vma->obj) !=
> > +		   i915_gem_object_is_lmem(ce->ring->vma->obj));
> > +
> > +	context_registered = lrc_desc_registered(guc, desc_idx);
> > +
> > +	reset_lrc_desc(guc, desc_idx);
> > +	set_lrc_desc_registered(guc, desc_idx, ce);
> > +
> > +	desc = __get_lrc_desc(guc, desc_idx);
> > +	desc->engine_class = engine_class_to_guc_class(engine->class);
> > +	desc->engine_submit_mask = adjust_engine_mask(engine->class,
> > +						      engine->mask);
> > +	desc->hw_context_desc = ce->lrc.lrca;
> > +	desc->priority = GUC_CLIENT_PRIORITY_KMD_NORMAL;
> > +	desc->context_flags = CONTEXT_REGISTRATION_FLAG_KMD;
> > +	guc_context_policy_init(engine, desc);
> > +	init_sched_state(ce);
> > +
> > +	/*
> > +	 * The context_lookup xarray is used to determine if the hardware
> > +	 * context is currently registered. There are two cases in which it
> > +	 * could be regisgered either the guc_id has been stole from from
> 
> typo regisgered
>

John got this one. Fixed.
 
> > +	 * another context or the lrc descriptor address of this context has
> > +	 * changed. In either case the context needs to be deregistered with the
> > +	 * GuC before registering this context.
> > +	 */
> > +	if (context_registered) {
> > +		set_context_wait_for_deregister_to_register(ce);
> > +		intel_context_get(ce);
> > +
> > +		/*
> > +		 * If stealing the guc_id, this ce has the same guc_id as the
> > +		 * context whos guc_id was stole.
> > +		 */
> > +		with_intel_runtime_pm(runtime_pm, wakeref)
> > +			ret = deregister_context(ce, ce->guc_id);
> > +	} else {
> > +		with_intel_runtime_pm(runtime_pm, wakeref)
> > +			ret = register_context(ce);
> > +	}
> > +
> > +	return ret;
> >   }
> >   static int guc_context_pre_pin(struct intel_context *ce,
> > @@ -443,36 +813,139 @@ static int guc_context_pre_pin(struct intel_context *ce,
> >   static int guc_context_pin(struct intel_context *ce, void *vaddr)
> >   {
> > +	if (i915_ggtt_offset(ce->state) !=
> > +	    (ce->lrc.lrca & CTX_GTT_ADDRESS_MASK))
> > +		set_bit(CONTEXT_LRCA_DIRTY, &ce->flags);
> 
> Shouldn't this be set after lrc_pin()? I can see ce->lrc.lrca being
> re-assigned in there; it looks like it can only change if the context is
> new, but for future-proofing IMO better to re-order here.
> 

No this is right. ce->state is assigned in lr_pre_pin and ce->lrc.lrca is
assigned in lrc_pin. To catch the change you have to check between
those two functions.

> > +
> >   	return lrc_pin(ce, ce->engine, vaddr);
> 
> Could use a comment to say that the GuC context pinning call is delayed
> until request alloc and to look at the comment in the latter function for
> details (or move the explanation here and refer here from request alloc).
>

Yes.
 
> >   }
> > +static void guc_context_unpin(struct intel_context *ce)
> > +{
> > +	struct intel_guc *guc = ce_to_guc(ce);
> > +
> > +	unpin_guc_id(guc, ce);
> > +	lrc_unpin(ce);
> > +}
> > +
> > +static void guc_context_post_unpin(struct intel_context *ce)
> > +{
> > +	lrc_post_unpin(ce);
> 
> why do we need this function? we can just pass lrc_post_unpin to the ops
> (like we already do).
> 

We don't before style reasons I think having a GuC specific wrapper is
correct.

> > +}
> > +
> > +static inline void guc_lrc_desc_unpin(struct intel_context *ce)
> > +{
> > +	struct intel_engine_cs *engine = ce->engine;
> > +	struct intel_guc *guc = &engine->gt->uc.guc;
> > +	unsigned long flags;
> > +
> > +	GEM_BUG_ON(!lrc_desc_registered(guc, ce->guc_id));
> > +	GEM_BUG_ON(ce != __get_context(guc, ce->guc_id));
> > +
> > +	spin_lock_irqsave(&ce->guc_state.lock, flags);
> > +	set_context_destroyed(ce);
> > +	spin_unlock_irqrestore(&ce->guc_state.lock, flags);
> > +
> > +	deregister_context(ce, ce->guc_id);
> > +}
> > +
> > +static void guc_context_destroy(struct kref *kref)
> > +{
> > +	struct intel_context *ce = container_of(kref, typeof(*ce), ref);
> > +	struct intel_runtime_pm *runtime_pm = &ce->engine->gt->i915->runtime_pm;
> 
> same as above, going through engine->uncore->rpm is shorter
>

Sure.
 
> > +	struct intel_guc *guc = &ce->engine->gt->uc.guc;
> > +	intel_wakeref_t wakeref;
> > +	unsigned long flags;
> > +
> > +	/*
> > +	 * If the guc_id is invalid this context has been stolen and we can free
> > +	 * it immediately. Also can be freed immediately if the context is not
> > +	 * registered with the GuC.
> > +	 */
> > +	if (context_guc_id_invalid(ce) ||
> > +	    !lrc_desc_registered(guc, ce->guc_id)) {
> > +		release_guc_id(guc, ce);
> 
> it feels a bit weird that we call release_guc_id in the case where the id is
> invalid. The code handles it fine, but still the flow doesn't feel clean.
> Not a blocker.
> 

I understand. Let's see if this can get cleaned up at some point.

> > +		lrc_destroy(kref);
> > +		return;
> > +	}
> > +
> > +	/*
> > +	 * We have to acquire the context spinlock and check guc_id again, if it
> > +	 * is valid it hasn't been stolen and needs to be deregistered. We
> > +	 * delete this context from the list of unpinned guc_ids available to
> > +	 * stole to seal a race with guc_lrc_desc_pin(). When the G2H CTB
> > +	 * returns indicating this context has been deregistered the guc_id is
> > +	 * returned to the pool of available guc_ids.
> > +	 */
> > +	spin_lock_irqsave(&guc->contexts_lock, flags);
> > +	if (context_guc_id_invalid(ce)) {
> > +		__release_guc_id(guc, ce);
> 
> But here the call to __release_guc_id is unneded, right? the ce doesn't own
> the ID anymore and both the steal and the release function already clean
> ce->guc_id_link, so there should be nothing left to clean.
>

This is dead code. Will delete.

> > +		spin_unlock_irqrestore(&guc->contexts_lock, flags);
> > +		lrc_destroy(kref);
> > +		return;
> > +	}
> > +
> > +	if (!list_empty(&ce->guc_id_link))
> > +		list_del_init(&ce->guc_id_link);
> > +	spin_unlock_irqrestore(&guc->contexts_lock, flags);
> > +
> > +	/*
> > +	 * We defer GuC context deregistration until the context is destroyed
> > +	 * in order to save on CTBs. With this optimization ideally we only need
> > +	 * 1 CTB to register the context during the first pin and 1 CTB to
> > +	 * deregister the context when the context is destroyed. Without this
> > +	 * optimization, a CTB would be needed every pin & unpin.
> > +	 *
> > +	 * XXX: Need to acqiure the runtime wakeref as this can be triggered
> > +	 * from context_free_worker when not runtime wakeref is held.
> > +	 * guc_lrc_desc_unpin requires the runtime as a GuC register is written
> > +	 * in H2G CTB to deregister the context. A future patch may defer this
> > +	 * H2G CTB if the runtime wakeref is zero.
> > +	 */
> > +	with_intel_runtime_pm(runtime_pm, wakeref)
> > +		guc_lrc_desc_unpin(ce);
> > +}
> > +
> > +static int guc_context_alloc(struct intel_context *ce)
> > +{
> > +	return lrc_alloc(ce, ce->engine);
> > +}
> > +
> >   static const struct intel_context_ops guc_context_ops = {
> >   	.alloc = guc_context_alloc,
> >   	.pre_pin = guc_context_pre_pin,
> >   	.pin = guc_context_pin,
> > -	.unpin = lrc_unpin,
> > -	.post_unpin = lrc_post_unpin,
> > +	.unpin = guc_context_unpin,
> > +	.post_unpin = guc_context_post_unpin,
> >   	.enter = intel_context_enter_engine,
> >   	.exit = intel_context_exit_engine,
> >   	.reset = lrc_reset,
> > -	.destroy = lrc_destroy,
> > +	.destroy = guc_context_destroy,
> >   };
> > -static int guc_request_alloc(struct i915_request *request)
> > +static bool context_needs_register(struct intel_context *ce, bool new_guc_id)
> >   {
> > +	return new_guc_id || test_bit(CONTEXT_LRCA_DIRTY, &ce->flags) ||
> > +		!lrc_desc_registered(ce_to_guc(ce), ce->guc_id);
> > +}
> > +
> > +static int guc_request_alloc(struct i915_request *rq)
> > +{
> > +	struct intel_context *ce = rq->context;
> > +	struct intel_guc *guc = ce_to_guc(ce);
> >   	int ret;
> > -	GEM_BUG_ON(!intel_context_is_pinned(request->context));
> > +	GEM_BUG_ON(!intel_context_is_pinned(rq->context));
> >   	/*
> >   	 * Flush enough space to reduce the likelihood of waiting after
> >   	 * we start building the request - in which case we will just
> >   	 * have to repeat work.
> >   	 */
> > -	request->reserved_space += GUC_REQUEST_SIZE;
> > +	rq->reserved_space += GUC_REQUEST_SIZE;
> >   	/*
> >   	 * Note that after this point, we have committed to using
> > @@ -483,56 +956,47 @@ static int guc_request_alloc(struct i915_request *request)
> >   	 */
> >   	/* Unconditionally invalidate GPU caches and TLBs. */
> > -	ret = request->engine->emit_flush(request, EMIT_INVALIDATE);
> > +	ret = rq->engine->emit_flush(rq, EMIT_INVALIDATE);
> >   	if (ret)
> >   		return ret;
> > -	request->reserved_space -= GUC_REQUEST_SIZE;
> > -	return 0;
> > -}
> > +	rq->reserved_space -= GUC_REQUEST_SIZE;
> > -static inline void queue_request(struct i915_sched_engine *sched_engine,
> > -				 struct i915_request *rq,
> > -				 int prio)
> > -{
> > -	GEM_BUG_ON(!list_empty(&rq->sched.link));
> > -	list_add_tail(&rq->sched.link,
> > -		      i915_sched_lookup_priolist(sched_engine, prio));
> > -	set_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);
> > -}
> > -
> > -static int guc_bypass_tasklet_submit(struct intel_guc *guc,
> > -				     struct i915_request *rq)
> > -{
> > -	int ret;
> > -
> > -	__i915_request_submit(rq);
> > -
> > -	trace_i915_request_in(rq, 0);
> > -
> > -	guc_set_lrc_tail(rq);
> > -	ret = guc_add_request(guc, rq);
> > -	if (ret == -EBUSY)
> > -		guc->stalled_request = rq;
> > -
> > -	return ret;
> > -}
> > -
> > -static void guc_submit_request(struct i915_request *rq)
> > -{
> > -	struct i915_sched_engine *sched_engine = rq->engine->sched_engine;
> > -	struct intel_guc *guc = &rq->engine->gt->uc.guc;
> > -	unsigned long flags;
> > +	/*
> > +	 * Call pin_guc_id here rather than in the pinning step as with
> > +	 * dma_resv, contexts can be repeatedly pinned / unpinned trashing the
> > +	 * guc_ids and creating horrible race conditions. This is especially bad
> > +	 * when guc_ids are being stolen due to over subscription. By the time
> > +	 * this function is reached, it is guaranteed that the guc_id will be
> > +	 * persistent until the generated request is retired. Thus, sealing these
> > +	 * race conditions. It is still safe to fail here if guc_ids are
> > +	 * exhausted and return -EAGAIN to the user indicating that they can try
> > +	 * again in the future.
> > +	 *
> > +	 * There is no need for a lock here as the timeline mutex ensures at
> > +	 * most one context can be executing this code path at once. The
> > +	 * guc_id_ref is incremented once for every request in flight and
> > +	 * decremented on each retire. When it is zero, a lock around the
> > +	 * increment (in pin_guc_id) is needed to seal a race with unpin_guc_id.
> > +	 */
> > +	if (atomic_add_unless(&ce->guc_id_ref, 1, 0))
> > +		return 0;
> > -	/* Will be called from irq-context when using foreign fences. */
> > -	spin_lock_irqsave(&sched_engine->lock, flags);
> > +	ret = pin_guc_id(guc, ce);	/* returns 1 if new guc_id assigned */
> > +	if (unlikely(ret < 0))
> > +		return ret;;
> 
> typo ";;"
> 

Yep.

> > +	if (context_needs_register(ce, !!ret)) {
> > +		ret = guc_lrc_desc_pin(ce);
> > +		if (unlikely(ret)) {	/* unwind */
> > +			atomic_dec(&ce->guc_id_ref);
> > +			unpin_guc_id(guc, ce);
> > +			return ret;
> > +		}
> > +	}
> > -	if (guc->stalled_request || !i915_sched_engine_is_empty(sched_engine))
> > -		queue_request(sched_engine, rq, rq_prio(rq));
> > -	else if (guc_bypass_tasklet_submit(guc, rq) == -EBUSY)
> > -		tasklet_hi_schedule(&sched_engine->tasklet);
> > +	clear_bit(CONTEXT_LRCA_DIRTY, &ce->flags);
> 
> 
> Might be worth moving the pinning to a separate function to keep the
> request_alloc focused on the request. Can be done as a follow up.
>

Sure. Let me see how that looks in a follow up.
 
> > -	spin_unlock_irqrestore(&sched_engine->lock, flags);
> > +	return 0;
> >   }
> >   static void sanitize_hwsp(struct intel_engine_cs *engine)
> > @@ -606,6 +1070,46 @@ static void guc_set_default_submission(struct intel_engine_cs *engine)
> >   	engine->submit_request = guc_submit_request;
> >   }
> > +static inline void guc_kernel_context_pin(struct intel_guc *guc,
> > +					  struct intel_context *ce)
> > +{
> > +	if (context_guc_id_invalid(ce))
> > +		pin_guc_id(guc, ce);
> > +	guc_lrc_desc_pin(ce);
> > +}
> > +
> > +static inline void guc_init_lrc_mapping(struct intel_guc *guc)
> > +{
> > +	struct intel_gt *gt = guc_to_gt(guc);
> > +	struct intel_engine_cs *engine;
> > +	enum intel_engine_id id;
> > +
> > +	/* make sure all descriptors are clean... */
> > +	xa_destroy(&guc->context_lookup);
> > +
> > +	/*
> > +	 * Some contexts might have been pinned before we enabled GuC
> > +	 * submission, so we need to add them to the GuC bookeeping.
> > +	 * Also, after a reset the GuC we want to make sure that the information
> > +	 * shared with GuC is properly reset. The kernel lrcs are not attached
> > +	 * to the gem_context, so they need to be added separately.
> > +	 *
> > +	 * Note: we purposely do not check the error return of
> > +	 * guc_lrc_desc_pin, because that function can only fail in two cases.
> > +	 * One, if there aren't enough free IDs, but we're guaranteed to have
> > +	 * enough here (we're either only pinning a handful of lrc on first boot
> > +	 * or we're re-pinning lrcs that were already pinned before the reset).
> > +	 * Two, if the GuC has died and CTBs can't make forward progress.
> > +	 * Presumably, the GuC should be alive as this function is called on
> > +	 * driver load or after a reset. Even if it is dead, another full GPU
> > +	 * reset will be triggered and this function would be called again.
> > +	 */
> > +
> > +	for_each_engine(engine, gt, id)
> > +		if (engine->kernel_context)
> > +			guc_kernel_context_pin(guc, engine->kernel_context);
> > +}
> > +
> >   static void guc_release(struct intel_engine_cs *engine)
> >   {
> >   	engine->sanitize = NULL; /* no longer in control, nothing to sanitize */
> > @@ -718,6 +1222,7 @@ int intel_guc_submission_setup(struct intel_engine_cs *engine)
> >   void intel_guc_submission_enable(struct intel_guc *guc)
> >   {
> > +	guc_init_lrc_mapping(guc);
> >   }
> >   void intel_guc_submission_disable(struct intel_guc *guc)
> > @@ -743,3 +1248,62 @@ void intel_guc_submission_init_early(struct intel_guc *guc)
> >   {
> >   	guc->submission_selected = __guc_submission_selected(guc);
> >   }
> > +
> > +static inline struct intel_context *
> > +g2h_context_lookup(struct intel_guc *guc, u32 desc_idx)
> > +{
> > +	struct intel_context *ce;
> > +
> > +	if (unlikely(desc_idx >= GUC_MAX_LRC_DESCRIPTORS)) {
> > +		drm_dbg(&guc_to_gt(guc)->i915->drm,
> > +			"Invalid desc_idx %u", desc_idx);
> > +		return NULL;
> > +	}
> > +
> > +	ce = __get_context(guc, desc_idx);
> > +	if (unlikely(!ce)) {
> > +		drm_dbg(&guc_to_gt(guc)->i915->drm,
> > +			"Context is NULL, desc_idx %u", desc_idx);
> > +		return NULL;
> > +	}
> > +
> > +	return ce;
> > +}
> > +
> > +int intel_guc_deregister_done_process_msg(struct intel_guc *guc,
> > +					  const u32 *msg,
> > +					  u32 len)
> > +{
> > +	struct intel_context *ce;
> > +	u32 desc_idx = msg[0];
> > +
> > +	if (unlikely(len < 1)) {
> > +		drm_dbg(&guc_to_gt(guc)->i915->drm, "Invalid length %u", len);
> > +		return -EPROTO;
> > +	}
> > +
> > +	ce = g2h_context_lookup(guc, desc_idx);
> > +	if (unlikely(!ce))
> > +		return -EPROTO;
> > +
> > +	if (context_wait_for_deregister_to_register(ce)) {
> > +		struct intel_runtime_pm *runtime_pm =
> > +			&ce->engine->gt->i915->runtime_pm;
> > +		intel_wakeref_t wakeref;
> > +
> > +		/*
> > +		 * Previous owner of this guc_id has been deregistered, now safe
> > +		 * register this context.
> > +		 */
> > +		with_intel_runtime_pm(runtime_pm, wakeref)
> > +			register_context(ce);
> > +		clr_context_wait_for_deregister_to_register(ce);
> > +		intel_context_put(ce);
> > +	} else if (context_destroyed(ce)) {
> > +		/* Context has been destroyed */
> > +		release_guc_id(guc, ce);
> > +		lrc_destroy(&ce->ref);
> > +	}
> > +
> > +	return 0;
> > +}
> > diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> > index 943fe485c662..204c95c39353 100644
> > --- a/drivers/gpu/drm/i915/i915_reg.h
> > +++ b/drivers/gpu/drm/i915/i915_reg.h
> > @@ -4142,6 +4142,7 @@ enum {
> >   	FAULT_AND_CONTINUE /* Unsupported */
> >   };
> > +#define CTX_GTT_ADDRESS_MASK GENMASK(31, 12)
> >   #define GEN8_CTX_VALID (1 << 0)
> >   #define GEN8_CTX_FORCE_PD_RESTORE (1 << 1)
> >   #define GEN8_CTX_FORCE_RESTORE (1 << 2)
> > diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> > index 86b4c9f2613d..b48c4905d3fc 100644
> > --- a/drivers/gpu/drm/i915/i915_request.c
> > +++ b/drivers/gpu/drm/i915/i915_request.c
> > @@ -407,6 +407,7 @@ bool i915_request_retire(struct i915_request *rq)
> >   	 */
> >   	if (!list_empty(&rq->sched.link))
> >   		remove_from_engine(rq);
> > +	atomic_dec(&rq->context->guc_id_ref);
> 
> Does this work/make sense  if GuC is disabled?
> 

It doesn't matter if the GuC is disabled as this var isn't used if it
is. A following patch adds a vfunc here and pushes this in the GuC
backend.

Matt

> Daniele
> 
> >   	GEM_BUG_ON(!llist_empty(&rq->execute_cb));
> >   	__list_del_entry(&rq->link); /* poison neither prev/next (RCU walks) */
> 
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