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

Arun Siluvery
2015-06-19T18:07:08Z

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>
---
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