Re: [PATCH v2 2/2] drm/vkms: Implement CRC debugfs API

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On Thu, Aug 02, 2018 at 08:09:51AM -0300, Gustavo Padovan wrote:
> Hi Haneen,
> 
> On Thu, Aug 02, 2018 at 04:10:26AM +0300, Haneen Mohammed wrote:
> > This patch implement the necessary functions to compute and add CRCs
> > entries:
> > 
> > - Implement the set_crc_source() callback.
> > - Compute CRC using crc32 on the visible part of the framebuffer.
> > - Use ordered workqueue per output to compute and add CRC at the end
> >   of a vblank.
> > - Use appropriate synchronization methods since the CRC computation must
> >   be atomic wrt the generated vblank event for a given atomic update, by
> >   using spinlock across atomic_begin/atomic_flush to wrap the event
> >   handling code completely and match the flip event with the CRC.
> > 
> > Since vkms_crc_work_handle() can sleep, spinlock can't be acquired
> > while accessing vkms_output->primary_crc to compute CRC.
> > To make sure the data is updated and released without conflict with
> > the vkms_crc_work_handle(), the work_struct is flushed @crtc_destroy
> > and the data is updated before scheduling the work handle again, as
> > follow:
> 
> I'm not sure I get why this is a spinlock and not a mutex. With the
> later you are able to sleep. Also, your spinlock held through the whole
> atomic commit (from the begin to flush) which seems too much time for
> busy waiting. Or am I missing something here?

I expressed some of the same concerns here:

https://lists.freedesktop.org/archives/dri-devel/2018-July/183584.html

The tl;dr is that the spinlock is required so we can acquire it in the vblank
hrtimer. It is held across begin/flush to prevent sending vblank eventss until
the crc has been fully calculated for the frame. More details in the thread,
ofc.

Sean

> 
> Gustavo
> 
> > 
> > * CRC data update:
> > 1- store vkms_crc_data {fb, src} per plane_state
> > 2- @plane_duplicate_state -> allocate vkms_crc_data
> > 3- during atomic commit (@atomic_update) ->
> > 	a) copy {fb, src} to plane_state->crc_data
> > 	b) get reference to fb,
> > 3- @plane_destroy_state -> a) if (fb refcount) remove reference to fb
> > 			   b) deallocate crc_data
> > 
> > * Atomic Commit:
> > 1- vkms_plane_atomic_check
> > 2- vkms_prepare_fb -> vmap vkms_gem_obj->vaddr
> > 3- atomic_begin -> hold crc spinlock
> > 4- atomic_plane_update -> a) update vkms_output->primary_crc
> > 			  b) get reference to fb
> > 5- atomic_flush -> a) send vblank event while holding event_lock
> > 		   b) release crc spinlock
> > 
> > * hrtimer regular callback:
> > 1- hold crc spinlock
> > 2- drm_crtc_handle_vblank()
> > 3- queue vkms_crc_work_handle
> > 4- release crc spinlock
> > 
> > * cleanup:
> > 1- @cleanup_fb ->vunmap vkms_gem_obj->vaddr
> > 2- @crtc_destroy -> flush work struct
> > 3- @plane_destroy -> a) if (fb refcount) remove reference to fb
> > 		     b) deallocate crc_data
> > 
> > Signed-off-by: Haneen Mohammed <hamohammed.sa@xxxxxxxxx>
> > ---
> > Changes in v2: 
> > - remove vkms_crc_data for primary plane from vkms_output
> >   and access it from vkms_plane_state instead.
> > - flush crc_workq in vkms_set_crc_source before changing out->enabled
> >   value.
> > 
> >  drivers/gpu/drm/vkms/Makefile     |  2 +-
> >  drivers/gpu/drm/vkms/vkms_crc.c   | 95 +++++++++++++++++++++++++++++++
> >  drivers/gpu/drm/vkms/vkms_crtc.c  | 56 +++++++++++++++---
> >  drivers/gpu/drm/vkms/vkms_drv.c   |  1 +
> >  drivers/gpu/drm/vkms/vkms_drv.h   | 21 +++++++
> >  drivers/gpu/drm/vkms/vkms_plane.c | 30 ++++++++++
> >  6 files changed, 196 insertions(+), 9 deletions(-)
> >  create mode 100644 drivers/gpu/drm/vkms/vkms_crc.c
> > 
> > diff --git a/drivers/gpu/drm/vkms/Makefile b/drivers/gpu/drm/vkms/Makefile
> > index 986297da51bf..37966914f70b 100644
> > --- a/drivers/gpu/drm/vkms/Makefile
> > +++ b/drivers/gpu/drm/vkms/Makefile
> > @@ -1,3 +1,3 @@
> > -vkms-y := vkms_drv.o vkms_plane.o vkms_output.o vkms_crtc.o vkms_gem.o
> > +vkms-y := vkms_drv.o vkms_plane.o vkms_output.o vkms_crtc.o vkms_gem.o vkms_crc.o
> >  
> >  obj-$(CONFIG_DRM_VKMS) += vkms.o
> > diff --git a/drivers/gpu/drm/vkms/vkms_crc.c b/drivers/gpu/drm/vkms/vkms_crc.c
> > new file mode 100644
> > index 000000000000..9b909221943f
> > --- /dev/null
> > +++ b/drivers/gpu/drm/vkms/vkms_crc.c
> > @@ -0,0 +1,95 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +#include "vkms_drv.h"
> > +#include <linux/crc32.h>
> > +#include <drm/drm_gem_framebuffer_helper.h>
> > +
> > +static uint32_t _vkms_get_crc(struct vkms_crc_data *crc_data)
> > +{
> > +	struct drm_framebuffer *fb = &crc_data->fb;
> > +	struct drm_gem_object *gem_obj = drm_gem_fb_get_obj(fb, 0);
> > +	struct vkms_gem_object *vkms_obj = drm_gem_to_vkms_gem(gem_obj);
> > +	u32 crc = 0;
> > +	int i = 0;
> > +	unsigned int x = crc_data->src.x1 >> 16;
> > +	unsigned int y = crc_data->src.y1 >> 16;
> > +	unsigned int height = drm_rect_height(&crc_data->src) >> 16;
> > +	unsigned int width = drm_rect_width(&crc_data->src) >> 16;
> > +	unsigned int cpp = fb->format->cpp[0];
> > +	unsigned int src_offset;
> > +	unsigned int size_byte = width * cpp;
> > +	void *vaddr;
> > +
> > +	mutex_lock(&vkms_obj->pages_lock);
> > +	vaddr = vkms_obj->vaddr;
> > +	if (WARN_ON(!vaddr))
> > +		return crc;
> > +
> > +	for (i = y; i < y + height; i++) {
> > +		src_offset = fb->offsets[0] + (i * fb->pitches[0]) + (x * cpp);
> > +		crc = crc32_le(crc, vaddr + src_offset, size_byte);
> > +	}
> > +	mutex_unlock(&vkms_obj->pages_lock);
> > +
> > +	return crc;
> > +}
> > +
> > +void vkms_crc_work_handle(struct work_struct *work)
> > +{
> > +	struct vkms_crtc_state *crtc_state = container_of(work,
> > +						struct vkms_crtc_state,
> > +						crc_work);
> > +	struct drm_crtc *crtc = crtc_state->base.crtc;
> > +	struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
> > +	struct vkms_device *vdev = container_of(out, struct vkms_device,
> > +						output);
> > +	struct vkms_crc_data *primary_crc = NULL;
> > +	struct drm_plane *plane;
> > +
> > +	u32 crc32 = 0;
> > +
> > +	drm_for_each_plane(plane, &vdev->drm) {
> > +		struct vkms_plane_state *vplane_state;
> > +		struct vkms_crc_data *crc_data;
> > +
> > +		vplane_state = to_vkms_plane_state(plane->state);
> > +		crc_data = vplane_state->crc_data;
> > +
> > +		if (drm_framebuffer_read_refcount(&crc_data->fb) == 0)
> > +			continue;
> > +
> > +		if (plane->type == DRM_PLANE_TYPE_PRIMARY) {
> > +			primary_crc = crc_data;
> > +			break;
> > +		}
> > +	}
> > +
> > +	if (primary_crc)
> > +		crc32 = _vkms_get_crc(primary_crc);
> > +
> > +	drm_crtc_add_crc_entry(crtc, true, crtc_state->n_frame, &crc32);
> > +}
> > +
> > +int vkms_set_crc_source(struct drm_crtc *crtc, const char *src_name,
> > +			size_t *values_cnt)
> > +{
> > +	struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
> > +	bool enabled = false;
> > +	unsigned long flags;
> > +	int ret = 0;
> > +
> > +	if (src_name && strcmp(src_name, "auto") == 0)
> > +		enabled = true;
> > +	else if (src_name)
> > +		ret = -EINVAL;
> > +
> > +	*values_cnt = 1;
> > +
> > +	/* make sure nothing is scheduled on crtc workq */
> > +	flush_workqueue(out->crc_workq);
> > +
> > +	spin_lock_irqsave(&out->lock, flags);
> > +	out->crc_enabled = enabled;
> > +	spin_unlock_irqrestore(&out->lock, flags);
> > +
> > +	return ret;
> > +}
> > diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c
> > index 26babb85ca77..a6c080d7f7ae 100644
> > --- a/drivers/gpu/drm/vkms/vkms_crtc.c
> > +++ b/drivers/gpu/drm/vkms/vkms_crtc.c
> > @@ -10,18 +10,33 @@
> >  #include <drm/drm_atomic_helper.h>
> >  #include <drm/drm_crtc_helper.h>
> >  
> > -static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
> > +static void _vblank_handle(struct vkms_output *output)
> >  {
> > -	struct vkms_output *output = container_of(timer, struct vkms_output,
> > -						  vblank_hrtimer);
> >  	struct drm_crtc *crtc = &output->crtc;
> > -	int ret_overrun;
> > +	struct vkms_crtc_state *state = to_vkms_crtc_state(crtc->state);
> >  	bool ret;
> >  
> > +	spin_lock(&output->lock);
> >  	ret = drm_crtc_handle_vblank(crtc);
> >  	if (!ret)
> >  		DRM_ERROR("vkms failure on handling vblank");
> >  
> > +	if (state && output->crc_enabled) {
> > +		state->n_frame = drm_crtc_accurate_vblank_count(crtc);
> > +		queue_work(output->crc_workq, &state->crc_work);
> > +	}
> > +
> > +	spin_unlock(&output->lock);
> > +}
> > +
> > +static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
> > +{
> > +	struct vkms_output *output = container_of(timer, struct vkms_output,
> > +						  vblank_hrtimer);
> > +	int ret_overrun;
> > +
> > +	_vblank_handle(output);
> > +
> >  	ret_overrun = hrtimer_forward_now(&output->vblank_hrtimer,
> >  					  output->period_ns);
> >  
> > @@ -97,18 +112,22 @@ vkms_atomic_crtc_duplicate_state(struct drm_crtc *crtc)
> >  
> >  	__drm_atomic_helper_crtc_duplicate_state(crtc, &vkms_state->base);
> >  
> > +	INIT_WORK(&vkms_state->crc_work, vkms_crc_work_handle);
> > +
> >  	return &vkms_state->base;
> >  }
> >  
> >  static void vkms_atomic_crtc_destroy_state(struct drm_crtc *crtc,
> >  					   struct drm_crtc_state *state)
> >  {
> > -	struct vkms_crtc_state *vkms_state;
> > -
> > -	vkms_state = to_vkms_crtc_state(state);
> > +	struct vkms_crtc_state *vkms_state = to_vkms_crtc_state(state);
> >  
> >  	__drm_atomic_helper_crtc_destroy_state(state);
> > -	kfree(vkms_state);
> > +
> > +	if (vkms_state) {
> > +		flush_work(&vkms_state->crc_work);
> > +		kfree(vkms_state);
> > +	}
> >  }
> >  
> >  static const struct drm_crtc_funcs vkms_crtc_funcs = {
> > @@ -120,6 +139,7 @@ static const struct drm_crtc_funcs vkms_crtc_funcs = {
> >  	.atomic_destroy_state   = vkms_atomic_crtc_destroy_state,
> >  	.enable_vblank		= vkms_enable_vblank,
> >  	.disable_vblank		= vkms_disable_vblank,
> > +	.set_crc_source		= vkms_set_crc_source,
> >  };
> >  
> >  static void vkms_crtc_atomic_enable(struct drm_crtc *crtc,
> > @@ -134,9 +154,21 @@ static void vkms_crtc_atomic_disable(struct drm_crtc *crtc,
> >  	drm_crtc_vblank_off(crtc);
> >  }
> >  
> > +static void vkms_crtc_atomic_begin(struct drm_crtc *crtc,
> > +				   struct drm_crtc_state *old_crtc_state)
> > +{
> > +	struct vkms_output *vkms_output = drm_crtc_to_vkms_output(crtc);
> > +
> > +	/* This lock is held across the atomic commit to block vblamk timer
> > +	 * from scheduling vkms_crc_work_handle until the crc_data is updated
> > +	 */
> > +	spin_lock_irq(&vkms_output->lock);
> > +}
> > +
> >  static void vkms_crtc_atomic_flush(struct drm_crtc *crtc,
> >  				   struct drm_crtc_state *old_crtc_state)
> >  {
> > +	struct vkms_output *vkms_output = drm_crtc_to_vkms_output(crtc);
> >  	unsigned long flags;
> >  
> >  	if (crtc->state->event) {
> > @@ -151,9 +183,12 @@ static void vkms_crtc_atomic_flush(struct drm_crtc *crtc,
> >  
> >  		crtc->state->event = NULL;
> >  	}
> > +
> > +	spin_unlock_irq(&vkms_output->lock);
> >  }
> >  
> >  static const struct drm_crtc_helper_funcs vkms_crtc_helper_funcs = {
> > +	.atomic_begin	= vkms_crtc_atomic_begin,
> >  	.atomic_flush	= vkms_crtc_atomic_flush,
> >  	.atomic_enable	= vkms_crtc_atomic_enable,
> >  	.atomic_disable	= vkms_crtc_atomic_disable,
> > @@ -162,6 +197,7 @@ static const struct drm_crtc_helper_funcs vkms_crtc_helper_funcs = {
> >  int vkms_crtc_init(struct drm_device *dev, struct drm_crtc *crtc,
> >  		   struct drm_plane *primary, struct drm_plane *cursor)
> >  {
> > +	struct vkms_output *vkms_out = drm_crtc_to_vkms_output(crtc);
> >  	int ret;
> >  
> >  	ret = drm_crtc_init_with_planes(dev, crtc, primary, cursor,
> > @@ -173,5 +209,9 @@ int vkms_crtc_init(struct drm_device *dev, struct drm_crtc *crtc,
> >  
> >  	drm_crtc_helper_add(crtc, &vkms_crtc_helper_funcs);
> >  
> > +	spin_lock_init(&vkms_out->lock);
> > +
> > +	vkms_out->crc_workq = alloc_ordered_workqueue("vkms_crc_workq", 0);
> > +
> >  	return ret;
> >  }
> > diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
> > index e340aa128b61..519a353cd909 100644
> > --- a/drivers/gpu/drm/vkms/vkms_drv.c
> > +++ b/drivers/gpu/drm/vkms/vkms_drv.c
> > @@ -79,6 +79,7 @@ static void vkms_release(struct drm_device *dev)
> >  	drm_atomic_helper_shutdown(&vkms->drm);
> >  	drm_mode_config_cleanup(&vkms->drm);
> >  	drm_dev_fini(&vkms->drm);
> > +	destroy_workqueue(vkms->output.crc_workq);
> >  }
> >  
> >  static struct drm_driver vkms_driver = {
> > diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> > index a1b206643c10..de1ddf31341b 100644
> > --- a/drivers/gpu/drm/vkms/vkms_drv.h
> > +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> > @@ -20,20 +20,31 @@ static const u32 vkms_formats[] = {
> >  	DRM_FORMAT_XRGB8888,
> >  };
> >  
> > +struct vkms_crc_data {
> > +	struct drm_rect src;
> > +	struct drm_framebuffer fb;
> > +};
> > +
> >  /**
> >   * vkms_plane_state - Driver specific plane state
> >   * @base: base plane state
> > + * @crc_data: data required for CRC computation
> >   */
> >  struct vkms_plane_state {
> >  	struct drm_plane_state base;
> > +	struct vkms_crc_data *crc_data;
> >  };
> >  
> >  /**
> >   * vkms_crtc_state - Driver specific CRTC state
> >   * @base: base CRTC state
> > + * @crc_work: work struct to compute and add CRC entries
> > + * @n_frame: frame number for computed CRC
> >   */
> >  struct vkms_crtc_state {
> >  	struct drm_crtc_state base;
> > +	struct work_struct crc_work;
> > +	unsigned int n_frame;
> >  };
> >  
> >  struct vkms_output {
> > @@ -43,6 +54,11 @@ struct vkms_output {
> >  	struct hrtimer vblank_hrtimer;
> >  	ktime_t period_ns;
> >  	struct drm_pending_vblank_event *event;
> > +	bool crc_enabled;
> > +	/* ordered wq for crc_work */
> > +	struct workqueue_struct *crc_workq;
> > +	/* protects concurrent access to crc_data */
> > +	spinlock_t lock;
> >  };
> >  
> >  struct vkms_device {
> > @@ -106,4 +122,9 @@ int vkms_gem_vmap(struct drm_gem_object *obj);
> >  
> >  void vkms_gem_vunmap(struct drm_gem_object *obj);
> >  
> > +/* CRC Support */
> > +int vkms_set_crc_source(struct drm_crtc *crtc, const char *src_name,
> > +			size_t *values_cnt);
> > +void vkms_crc_work_handle(struct work_struct *work);
> > +
> >  #endif /* _VKMS_DRV_H_ */
> > diff --git a/drivers/gpu/drm/vkms/vkms_plane.c b/drivers/gpu/drm/vkms/vkms_plane.c
> > index 70fca22bc51b..c91661631c76 100644
> > --- a/drivers/gpu/drm/vkms/vkms_plane.c
> > +++ b/drivers/gpu/drm/vkms/vkms_plane.c
> > @@ -16,11 +16,18 @@ static struct drm_plane_state *
> >  vkms_plane_duplicate_state(struct drm_plane *plane)
> >  {
> >  	struct vkms_plane_state *vkms_state;
> > +	struct vkms_crc_data *crc_data;
> >  
> >  	vkms_state = kzalloc(sizeof(*vkms_state), GFP_KERNEL);
> >  	if (!vkms_state)
> >  		return NULL;
> >  
> > +	crc_data = kzalloc(sizeof(*crc_data), GFP_KERNEL);
> > +	if (WARN_ON(!crc_data))
> > +		DRM_INFO("Couldn't allocate crc_data");
> > +
> > +	vkms_state->crc_data = crc_data;
> > +
> >  	__drm_atomic_helper_plane_duplicate_state(plane,
> >  						  &vkms_state->base);
> >  
> > @@ -31,6 +38,18 @@ static void vkms_plane_destroy_state(struct drm_plane *plane,
> >  				     struct drm_plane_state *old_state)
> >  {
> >  	struct vkms_plane_state *vkms_state = to_vkms_plane_state(old_state);
> > +	struct drm_crtc *crtc = vkms_state->base.crtc;
> > +
> > +	if (crtc) {
> > +		/* dropping the reference we acquired in
> > +		 * vkms_primary_plane_update()
> > +		 */
> > +		if (drm_framebuffer_read_refcount(&vkms_state->crc_data->fb))
> > +			drm_framebuffer_put(&vkms_state->crc_data->fb);
> > +	}
> > +
> > +	kfree(vkms_state->crc_data);
> > +	vkms_state->crc_data = NULL;
> >  
> >  	__drm_atomic_helper_plane_destroy_state(old_state);
> >  	kfree(vkms_state);
> > @@ -65,6 +84,17 @@ static const struct drm_plane_funcs vkms_plane_funcs = {
> >  static void vkms_primary_plane_update(struct drm_plane *plane,
> >  				      struct drm_plane_state *old_state)
> >  {
> > +	struct vkms_plane_state *vkms_plane_state;
> > +	struct vkms_crc_data *crc_data;
> > +
> > +	if (!plane->state->crtc || !plane->state->fb)
> > +		return;
> > +
> > +	vkms_plane_state = to_vkms_plane_state(plane->state);
> > +	crc_data = vkms_plane_state->crc_data;
> > +	memcpy(&crc_data->src, &plane->state->src, sizeof(struct drm_rect));
> > +	memcpy(&crc_data->fb, plane->state->fb, sizeof(struct drm_framebuffer));
> > +	drm_framebuffer_get(&crc_data->fb);
> >  }
> >  
> >  static int vkms_plane_atomic_check(struct drm_plane *plane,
> > -- 
> > 2.17.1
> > 

-- 
Sean Paul, Software Engineer, Google / Chromium OS
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