Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx> --- .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 99 ++++++++++++++----- 1 file changed, 77 insertions(+), 22 deletions(-) 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 337ddc0dab6b..594a99ea4f5c 100644 --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c @@ -29,21 +29,6 @@ /** * DOC: GuC-based command submission * - * IMPORTANT NOTE: GuC submission is currently not supported in i915. The GuC - * firmware is moving to an updated submission interface and we plan to - * turn submission back on when that lands. The below documentation (and related - * code) matches the old submission model and will be updated as part of the - * upgrade to the new flow. - * - * GuC stage descriptor: - * During initialization, the driver allocates a static pool of 1024 such - * descriptors, and shares them with the GuC. Currently, we only use one - * descriptor. This stage descriptor lets the GuC know about the workqueue and - * process descriptor. Theoretically, it also lets the GuC know about our HW - * contexts (context ID, etc...), but we actually employ a kind of submission - * where the GuC uses the LRCA sent via the work item instead. This is called - * a "proxy" submission. - * * The Scratch registers: * There are 16 MMIO-based registers start from 0xC180. The kernel driver writes * a value to the action register (SOFT_SCRATCH_0) along with any data. It then @@ -52,13 +37,45 @@ * processes the request. The kernel driver polls waiting for this update and * then proceeds. * - * Work Items: - * There are several types of work items that the host may place into a - * workqueue, each with its own requirements and limitations. Currently only - * WQ_TYPE_INORDER is needed to support legacy submission via GuC, which - * represents in-order queue. The kernel driver packs ring tail pointer and an - * ELSP context descriptor dword into Work Item. - * See gse_add_request() + * Command Transport buffers (CTBs): + * Covered in detail in other sections but CTBs (host-to-guc, H2G, guc-to-host + * G2H) are how the i915 controls submissions. + * + * Context registration: + * Before a context can be submitted it must be registered with the GuC via a + * H2G. A unique guc_id associated with each context. The context is either + * registered at request creation time (no flow control) or at submission time + * (flow control). It will stay registered until the context is destroyed or a + * flow control condition is met (e.g. pressure on guc_ids). + * + * Context submission: + * The i915 updates the LRC tail value in memory. Either a schedule enable H2G + * or context submit H2G is used to submit a context. + * + * Context unpin: + * To unpin a context a H2G is used to disable scheduling and when the + * corresponding G2H returns indicating the scheduling disable operation has + * completed it is safe to unpin the context. While a disable is in flight it + * isn't safe to resubmit the context so a fence is used to stall all future + * requests until the G2H is returned. + * + * Context deregistration: + * Before a context can be destroyed or we steal its guc_id we must deregister + * the context with the GuC via H2G. If stealing the guc_id it isn't safe to + * submit anything to this guc_id until the deregister completes so a fence is + * used to stall all requests associated with this guc_ids until the + * corresponding G2H returns indicating the guc_id has been deregistered. + * + * guc_ids: + * Unique number associated with private GuC context data passed in during + * context registration / submission / deregistration. 64k available. Simple ida + * is used for allocation. + * + * Stealing guc_ids: + * If no guc_ids are available they can be stolen from another context at + * request creation time if that context is unpinned. If nothing can be found at + * request creation time, flow control is triggered (serializing all submission + * until flow control exits) and guc_ids are stolden at submission time. * * GuC flow control state machine: * The tasklet, workqueue (retire_worker), and the G2H handlers together more or @@ -79,6 +96,44 @@ * STALL_MOVE_LRC_TAIL Tasklet will try to move LRC tail * STALL_ADD_REQUEST Tasklet will try to add the request (submit * context) + * + * Locking: + * In the GuC submission code we have 4 basic spin locks which protect + * everything. Details about each below. + * + * gse->sched_engine->lock + * This is the submission lock for all contexts that share a GuC submit engine + * (gse), thus only 1 context which share a gse can be submitting at a time. + * + * guc->contexts_lock + * Protects guc_id allocation. Global lock i.e. Only 1 context that uses GuC + * submission can hold this at a time. + * + * ce->guc_state.lock + * Protects everything under ce->guc_state. Ensures that a context is in the + * correct state before issuing a H2G. e.g. We don't issue a schedule disable + * on disabled context (bad idea), we don't issue schedule enable when a + * schedule disable is inflight, etc... Lock individual to each context. + * + * ce->guc_active.lock + * Protects everything under ce->guc_active which is the current requests + * inflight on the context / priority management. Lock individual to each + * context. + * + * Lock ordering rules: + * ce->guc_state.lock -> gse->sched_engine->lock -> ce->guc_active.lock + * gse->sched_engine->lock -> guc->contexts_lock + * + * Reset races: + * When a GPU full reset is triggered it is assumed that some G2H responses to + * a H2G can be lost as the GuC is likely toast. Losing these G2H can prove to + * fatal as we do certain operations upon receiving a G2H (e.g. destroy + * contexts, release guc_ids, etc...). Luckly when this occurs we can scrub + * context state and cleanup appropriately, however this is quite racey. To + * avoid races the rules are check for submission being disabled (i.e. check for + * mid reset) with the appropriate lock being held. If submission is disabled + * don't send the H2G. The reset code must disable submission and flush all + * locks before scrubbing for missing G2H. */ static struct intel_context * -- 2.28.0
