Re: [PATCH v6 1/6] drm/i915/gen8: Add infrastructure to initialize WA batch buffers

Daniel Vetter
2015-06-22T15:38:16Z

On Fri, Jun 19, 2015 at 07:07:01PM +0100, Arun Siluvery wrote:
> Some of the WA are to be applied during context save but before restore and
> some at the end of context save/restore but before executing the instructions
> in the ring, WA batch buffers are created for this purpose and these WA cannot
> be applied using normal means. Each context has two registers to load the
> offsets of these batch buffers. If they are non-zero, HW understands that it
> need to execute these batches.
>
> v1: In this version two separate ring_buffer objects were used to load WA
> instructions for indirect and per context batch buffers and they were part
> of every context.
>
> v2: Chris suggested to include additional page in context and use it to load
> these WA instead of creating separate objects. This will simplify lot of things
> as we need not explicity pin/unpin them. Thomas Daniel further pointed that GuC
> is planning to use a similar setup to share data between GuC and driver and
> WA batch buffers can probably share that page. However after discussions with
> Dave who is implementing GuC changes, he suggested to use an independent page
> for the reasons - GuC area might grow and these WA are initialized only once and
> are not changed afterwards so we can share them share across all contexts.
>
> The page is updated with WA during render ring init. This has an advantage of
> not adding more special cases to default_context.
>
> We don't know upfront the number of WA we will applying using these batch buffers.
> For this reason the size was fixed earlier but it is not a good idea. To fix this,
> the functions that load instructions are modified to report the no of commands
> inserted and the size is now calculated after the batch is updated. A macro is
> introduced to add commands to these batch buffers which also checks for overflow
> and returns error.
> We have a full page dedicated for these WA so that should be sufficient for
> good number of WA, anything more means we have major issues.
> The list for Gen8 is small, same for Gen9 also, maybe few more gets added
> going forward but not close to filling entire page. Chris suggested a two-pass
> approach but we agreed to go with single page setup as it is a one-off routine
> and simpler code wins.
>
> One additional option is offset field which is helpful if we would like to
> have multiple batches at different offsets within the page and select them
> based on some criteria. This is not a requirement at this point but could
> help in future (Dave).
>
> Chris provided some helpful macros and suggestions which further simplified
> the code, they will also help in reducing code duplication when WA for
> other Gen are added. Add detailed comments explaining restrictions.
> Use do {} while(0) for wa_ctx_emit() macro.
>
> (Many thanks to Chris, Dave and Thomas for their reviews and inputs)
>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Dave Gordon <david.s.gordon@intel.com>
> Signed-off-by: Rafael Barbalho <rafael.barbalho@intel.com>
> Signed-off-by: Arun Siluvery <arun.siluvery@linux.intel.com>
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

Why did you resend this one - I don't spot any updates in the commit
message? Also when resending please in-reply to the corresponding previous
version of that patch, not the cover letter of the series.
-Daniel

> ---
> drivers/gpu/drm/i915/intel_lrc.c | 223 +++++++++++++++++++++++++++++++-
> drivers/gpu/drm/i915/intel_ringbuffer.h | 21 +++
> 2 files changed, 240 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 0413b8f..0585298 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -211,6 +211,7 @@ enum {
> FAULT_AND_CONTINUE /* Unsupported */
> };
> #define GEN8_CTX_ID_SHIFT 32
> +#define CTX_RCS_INDIRECT_CTX_OFFSET_DEFAULT 0x17
>
> static int intel_lr_context_pin(struct intel_engine_cs *ring,
> struct intel_context *ctx);
> @@ -1077,6 +1078,191 @@ static int intel_logical_ring_workarounds_emit(struct intel_engine_cs *ring,
> return 0;
> }
>
> +#define wa_ctx_emit(batch, cmd) \
> + do { \
> + if (WARN_ON(index >= (PAGE_SIZE / sizeof(uint32_t)))) { \
> + return -ENOSPC; \
> + } \
> + batch[index++] = (cmd); \
> + } while (0)
> +
> +static inline uint32_t wa_ctx_start(struct i915_wa_ctx_bb *wa_ctx,
> + uint32_t offset,
> + uint32_t start_alignment)
> +{
> + return wa_ctx->offset = ALIGN(offset, start_alignment);
> +}
> +
> +static inline int wa_ctx_end(struct i915_wa_ctx_bb *wa_ctx,
> + uint32_t offset,
> + uint32_t size_alignment)
> +{
> + wa_ctx->size = offset - wa_ctx->offset;
> +
> + WARN(wa_ctx->size % size_alignment,
> + "wa_ctx_bb failed sanity checks: size %d is not aligned to %d\n",
> + wa_ctx->size, size_alignment);
> + return 0;
> +}
> +
> +/**
> + * gen8_init_indirectctx_bb() - initialize indirect ctx batch with WA
> + *
> + * @ring: only applicable for RCS
> + * @wa_ctx: structure representing wa_ctx
> + * offset: specifies start of the batch, should be cache-aligned. This is updated
> + * with the offset value received as input.
> + * size: size of the batch in DWORDS but HW expects in terms of cachelines
> + * @batch: page in which WA are loaded
> + * @offset: This field specifies the start of the batch, it should be
> + * cache-aligned otherwise it is adjusted accordingly.
> + * Typically we only have one indirect_ctx and per_ctx batch buffer which are
> + * initialized at the beginning and shared across all contexts but this field
> + * helps us to have multiple batches at different offsets and select them based
> + * on a criteria. At the moment this batch always start at the beginning of the page
> + * and at this point we don't have multiple wa_ctx batch buffers.
> + *
> + * The number of WA applied are not known at the beginning; we use this field
> + * to return the no of DWORDS written.
> +
> + * It is to be noted that this batch does not contain MI_BATCH_BUFFER_END
> + * so it adds NOOPs as padding to make it cacheline aligned.
> + * MI_BATCH_BUFFER_END will be added to perctx batch and both of them together
> + * makes a complete batch buffer.
> + *
> + * Return: non-zero if we exceed the PAGE_SIZE limit.
> + */
> +
> +static int gen8_init_indirectctx_bb(struct intel_engine_cs *ring,
> + struct i915_wa_ctx_bb *wa_ctx,
> + uint32_t *const batch,
> + uint32_t *offset)
> +{
> + uint32_t index = wa_ctx_start(wa_ctx, *offset, CACHELINE_DWORDS);
> +
> + /* FIXME: Replace me with WA */
> + wa_ctx_emit(batch, MI_NOOP);
> +
> + /* Pad to end of cacheline */
> + while (index % CACHELINE_DWORDS)
> + wa_ctx_emit(batch, MI_NOOP);
> +
> + /*
> + * MI_BATCH_BUFFER_END is not required in Indirect ctx BB because
> + * execution depends on the length specified in terms of cache lines
> + * in the register CTX_RCS_INDIRECT_CTX
> + */
> +
> + return wa_ctx_end(wa_ctx, *offset = index, CACHELINE_DWORDS);
> +}
> +
> +/**
> + * gen8_init_perctx_bb() - initialize per ctx batch with WA
> + *
> + * @ring: only applicable for RCS
> + * @wa_ctx: structure representing wa_ctx
> + * offset: specifies start of the batch, should be cache-aligned.
> + * size: size of the batch in DWORDS but HW expects in terms of cachelines
> + * @offset: This field specifies the start of this batch.
> + * This batch is started immediately after indirect_ctx batch. Since we ensure
> + * that indirect_ctx ends on a cacheline this batch is aligned automatically.
> + *
> + * The number of DWORDS written are returned using this field.
> + *
> + * This batch is terminated with MI_BATCH_BUFFER_END and so we need not add padding
> + * to align it with cacheline as padding after MI_BATCH_BUFFER_END is redundant.
> + */
> +static int gen8_init_perctx_bb(struct intel_engine_cs *ring,
> + struct i915_wa_ctx_bb *wa_ctx,
> + uint32_t *const batch,
> + uint32_t *offset)
> +{
> + uint32_t index = wa_ctx_start(wa_ctx, *offset, CACHELINE_DWORDS);
> +
> + wa_ctx_emit(batch, MI_BATCH_BUFFER_END);
> +
> + return wa_ctx_end(wa_ctx, *offset = index, 1);
> +}
> +
> +static int lrc_setup_wa_ctx_obj(struct intel_engine_cs *ring, u32 size)
> +{
> + int ret;
> +
> + ring->wa_ctx.obj = i915_gem_alloc_object(ring->dev, PAGE_ALIGN(size));
> + if (!ring->wa_ctx.obj) {
> + DRM_DEBUG_DRIVER("alloc LRC WA ctx backing obj failed.\n");
> + return -ENOMEM;
> + }
> +
> + ret = i915_gem_obj_ggtt_pin(ring->wa_ctx.obj, PAGE_SIZE, 0);
> + if (ret) {
> + DRM_DEBUG_DRIVER("pin LRC WA ctx backing obj failed: %d\n",
> + ret);
> + drm_gem_object_unreference(&ring->wa_ctx.obj->base);
> + return ret;
> + }
> +
> + return 0;
> +}
> +
> +static void lrc_destroy_wa_ctx_obj(struct intel_engine_cs *ring)
> +{
> + if (ring->wa_ctx.obj) {
> + i915_gem_object_ggtt_unpin(ring->wa_ctx.obj);
> + drm_gem_object_unreference(&ring->wa_ctx.obj->base);
> + ring->wa_ctx.obj = NULL;
> + }
> +}
> +
> +static int intel_init_workaround_bb(struct intel_engine_cs *ring)
> +{
> + int ret;
> + uint32_t *batch;
> + uint32_t offset;
> + struct page *page;
> + struct i915_ctx_workarounds *wa_ctx = &ring->wa_ctx;
> +
> + WARN_ON(ring->id != RCS);
> +
> + ret = lrc_setup_wa_ctx_obj(ring, PAGE_SIZE);
> + if (ret) {
> + DRM_DEBUG_DRIVER("Failed to setup context WA page: %d\n", ret);
> + return ret;
> + }
> +
> + page = i915_gem_object_get_page(wa_ctx->obj, 0);
> + batch = kmap_atomic(page);
> + offset = 0;
> +
> + if (INTEL_INFO(ring->dev)->gen == 8) {
> + ret = gen8_init_indirectctx_bb(ring,
> + &wa_ctx->indirect_ctx,
> + batch,
> + &offset);
> + if (ret)
> + goto out;
> +
> + ret = gen8_init_perctx_bb(ring,
> + &wa_ctx->per_ctx,
> + batch,
> + &offset);
> + if (ret)
> + goto out;
> + } else {
> + WARN(INTEL_INFO(ring->dev)->gen >= 8,
> + "WA batch buffer is not initialized for Gen%d\n",
> + INTEL_INFO(ring->dev)->gen);
> + lrc_destroy_wa_ctx_obj(ring);
> + }
> +
> +out:
> + kunmap_atomic(batch);
> + if (ret)
> + lrc_destroy_wa_ctx_obj(ring);
> +
> + return ret;
> +}
> +
> static int gen8_init_common_ring(struct intel_engine_cs *ring)
> {
> struct drm_device *dev = ring->dev;
> @@ -1411,6 +1597,8 @@ void intel_logical_ring_cleanup(struct intel_engine_cs *ring)
> kunmap(sg_page(ring->status_page.obj->pages->sgl));
> ring->status_page.obj = NULL;
> }
> +
> + lrc_destroy_wa_ctx_obj(ring);
> }
>
> static int logical_ring_init(struct drm_device *dev, struct intel_engine_cs *ring)
> @@ -1474,7 +1662,22 @@ static int logical_render_ring_init(struct drm_device *dev)
> if (ret)
> return ret;
>
> - return intel_init_pipe_control(ring);
> + ret = intel_init_workaround_bb(ring);
> + if (ret) {
> + /*
> + * We continue even if we fail to initialize WA batch
> + * because we only expect rare glitches but nothing
> + * critical to prevent us from using GPU
> + */
> + DRM_ERROR("WA batch buffer initialization failed: %d\n",
> + ret);
> + }
> +
> + ret = intel_init_pipe_control(ring);
> + if (ret)
> + lrc_destroy_wa_ctx_obj(ring);
> +
> + return ret;
> }
>
> static int logical_bsd_ring_init(struct drm_device *dev)
> @@ -1754,15 +1957,27 @@ populate_lr_context(struct intel_context *ctx, struct drm_i915_gem_object *ctx_o
> reg_state[CTX_SECOND_BB_STATE] = ring->mmio_base + 0x118;
> reg_state[CTX_SECOND_BB_STATE+1] = 0;
> if (ring->id == RCS) {
> - /* TODO: according to BSpec, the register state context
> - * for CHV does not have these. OTOH, these registers do
> - * exist in CHV. I'm waiting for a clarification */
> reg_state[CTX_BB_PER_CTX_PTR] = ring->mmio_base + 0x1c0;
> reg_state[CTX_BB_PER_CTX_PTR+1] = 0;
> reg_state[CTX_RCS_INDIRECT_CTX] = ring->mmio_base + 0x1c4;
> reg_state[CTX_RCS_INDIRECT_CTX+1] = 0;
> reg_state[CTX_RCS_INDIRECT_CTX_OFFSET] = ring->mmio_base + 0x1c8;
> reg_state[CTX_RCS_INDIRECT_CTX_OFFSET+1] = 0;
> + if (ring->wa_ctx.obj) {
> + struct i915_ctx_workarounds *wa_ctx = &ring->wa_ctx;
> + uint32_t ggtt_offset = i915_gem_obj_ggtt_offset(wa_ctx->obj);
> +
> + reg_state[CTX_RCS_INDIRECT_CTX+1] =
> + (ggtt_offset + wa_ctx->indirect_ctx.offset * sizeof(uint32_t)) |
> + (wa_ctx->indirect_ctx.size / CACHELINE_DWORDS);
> +
> + reg_state[CTX_RCS_INDIRECT_CTX_OFFSET+1] =
> + CTX_RCS_INDIRECT_CTX_OFFSET_DEFAULT << 6;
> +
> + reg_state[CTX_BB_PER_CTX_PTR+1] =
> + (ggtt_offset + wa_ctx->per_ctx.offset * sizeof(uint32_t)) |
> + 0x01;
> + }
> }
> reg_state[CTX_LRI_HEADER_1] = MI_LOAD_REGISTER_IMM(9);
> reg_state[CTX_LRI_HEADER_1] |= MI_LRI_FORCE_POSTED;
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
> index 39f6dfc..06467c6 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> @@ -12,6 +12,7 @@
> * workarounds!
> */
> #define CACHELINE_BYTES 64
> +#define CACHELINE_DWORDS (CACHELINE_BYTES / sizeof(uint32_t))
>
> /*
> * Gen2 BSpec "1. Programming Environment" / 1.4.4.6 "Ring Buffer Use"
> @@ -119,6 +120,25 @@ struct intel_ringbuffer {
>
> struct intel_context;
>
> +/*
> + * we use a single page to load ctx workarounds so all of these
> + * values are referred in terms of dwords
> + *
> + * struct i915_wa_ctx_bb:
> + * offset: specifies batch starting position, also helpful in case
> + * if we want to have multiple batches at different offsets based on
> + * some criteria. It is not a requirement at the moment but provides
> + * an option for future use.
> + * size: size of the batch in DWORDS
> + */
> +struct i915_ctx_workarounds {
> + struct i915_wa_ctx_bb {
> + u32 offset;
> + u32 size;
> + } indirect_ctx, per_ctx;
> + struct drm_i915_gem_object *obj;
> +};
> +
> struct intel_engine_cs {
> const char *name;
> enum intel_ring_id {
> @@ -142,6 +162,7 @@ struct intel_engine_cs {
> struct i915_gem_batch_pool batch_pool;
>
> struct intel_hw_status_page status_page;
> + struct i915_ctx_workarounds wa_ctx;
>
> unsigned irq_refcount; /* protected by dev_priv->irq_lock */
> u32 irq_enable_mask; /* bitmask to enable ring interrupt */
> --
> 2.3.0
>
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--
Daniel Vetter
Software Engineer, Intel Corporation