drm/i915/guc: Improve the GuC documentation & comments about proxy submissions
While at it, fix a typo (s/ring_lcra/ring_lrca) and improve the naming of one firware interface field (s/ring_tail/submit_element_info, since it can contain more than just the ring tail). No change in functionality. v2: - Remove reference to "unique user" of the GuC (Daniele) - Keep mention to renaming from "GuC context" to "client" (Daniele) Signed-off-by: Oscar Mateo <oscar.mateo@intel.com> Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com> Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
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@ -30,16 +30,25 @@
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/**
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* DOC: GuC-based command submission
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*
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* i915_guc_client:
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* We use the term client to avoid confusion with contexts. A i915_guc_client is
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* equivalent to GuC object guc_context_desc. This context descriptor is
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* allocated from a pool of 1024 entries. Kernel driver will allocate doorbell
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* and workqueue for it. Also the process descriptor (guc_process_desc), which
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* is mapped to client space. So the client can write Work Item then ring the
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* doorbell.
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* GuC client:
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* A i915_guc_client refers to a submission path through GuC. Currently, there
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* is only one of these (the execbuf_client) and this one is charged with all
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* submissions to the GuC. This struct is the owner of a doorbell, a process
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* descriptor and a workqueue (all of them inside a single gem object that
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* contains all required pages for these elements).
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*
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* To simplify the implementation, we allocate one gem object that contains all
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* pages for doorbell, process descriptor and workqueue.
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* GuC context descriptor:
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* During initialization, the driver allocates a static pool of 1024 such
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* descriptors, and shares them with the GuC.
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* Currently, there exists a 1:1 mapping between a i915_guc_client and a
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* guc_context_desc (via the client's context_index), so effectively only
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* one guc_context_desc gets used. This context descriptor lets the GuC know
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* about the doorbell, workqueue and process descriptor. Theoretically, it also
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* lets the GuC know about our HW contexts (Context ID, etc...), but we actually
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* employ a kind of submission where the GuC uses the LRCA sent via the work
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* item instead (the single guc_context_desc associated to execbuf client
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* contains information about the default kernel context only, but this is
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* essentially unused). This is called a "proxy" submission.
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*
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* The Scratch registers:
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* There are 16 MMIO-based registers start from 0xC180. The kernel driver writes
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@ -308,10 +317,17 @@ static void guc_ctx_desc_init(struct intel_guc *guc,
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if (!ce->state)
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break; /* XXX: continue? */
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/*
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* XXX: When this is a GUC_CTX_DESC_ATTR_KERNEL client (proxy
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* submission or, in other words, not using a direct submission
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* model) the KMD's LRCA is not used for any work submission.
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* Instead, the GuC uses the LRCA of the user mode context (see
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* guc_wq_item_append below).
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*/
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lrc->context_desc = lower_32_bits(ce->lrc_desc);
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/* The state page is after PPHWSP */
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lrc->ring_lcra =
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lrc->ring_lrca =
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guc_ggtt_offset(ce->state) + LRC_STATE_PN * PAGE_SIZE;
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lrc->context_id = (client->ctx_index << GUC_ELC_CTXID_OFFSET) |
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(guc_engine_id << GUC_ELC_ENGINE_OFFSET);
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@ -341,10 +357,6 @@ static void guc_ctx_desc_init(struct intel_guc *guc,
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desc->wq_addr = gfx_addr + client->wq_offset;
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desc->wq_size = client->wq_size;
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/*
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* XXX: Take LRCs from an existing context if this is not an
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* IsKMDCreatedContext client
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*/
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desc->desc_private = (uintptr_t)client;
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}
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@ -468,7 +480,7 @@ static void guc_wq_item_append(struct i915_guc_client *client,
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/* The GuC wants only the low-order word of the context descriptor */
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wqi->context_desc = (u32)intel_lr_context_descriptor(rq->ctx, engine);
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wqi->ring_tail = tail << WQ_RING_TAIL_SHIFT;
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wqi->submit_element_info = tail << WQ_RING_TAIL_SHIFT;
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wqi->fence_id = rq->global_seqno;
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}
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@ -251,7 +251,7 @@ union guc_doorbell_qw {
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struct guc_wq_item {
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u32 header;
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u32 context_desc;
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u32 ring_tail;
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u32 submit_element_info;
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u32 fence_id;
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} __packed;
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@ -278,7 +278,7 @@ struct guc_execlist_context {
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u32 context_desc;
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u32 context_id;
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u32 ring_status;
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u32 ring_lcra;
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u32 ring_lrca;
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u32 ring_begin;
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u32 ring_end;
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u32 ring_next_free_location;
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@ -34,7 +34,9 @@ struct drm_i915_gem_request;
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/*
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* This structure primarily describes the GEM object shared with the GuC.
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* The GEM object is held for the entire lifetime of our interaction with
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* The specs sometimes refer to this object as a "GuC context", but we use
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* the term "client" to avoid confusion with hardware contexts. This
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* GEM object is held for the entire lifetime of our interaction with
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* the GuC, being allocated before the GuC is loaded with its firmware.
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* Because there's no way to update the address used by the GuC after
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* initialisation, the shared object must stay pinned into the GGTT as
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@ -44,7 +46,7 @@ struct drm_i915_gem_request;
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*
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* The single GEM object described here is actually made up of several
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* separate areas, as far as the GuC is concerned. The first page (kept
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* kmap'd) includes the "process decriptor" which holds sequence data for
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* kmap'd) includes the "process descriptor" which holds sequence data for
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* the doorbell, and one cacheline which actually *is* the doorbell; a
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* write to this will "ring the doorbell" (i.e. send an interrupt to the
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* GuC). The subsequent pages of the client object constitute the work
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