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drm/msm/a5xx: workaround early ring-buffer emptiness check

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There is another cause for soft lock-up of GPU in empty ring-buffer:
race between GPU executing last commands and CPU checking ring for
emptiness. On GPU side IRQ for retire is triggered by CACHE_FLUSH_TS
event and RPTR shadow (which is used to check ring emptiness) is updated
a bit later from CP_CONTEXT_SWITCH_YIELD. Thus if GPU is executing its
last commands slow enough or we check that ring too fast we will miss a
chance to trigger switch to lower priority ring because current ring isn't
empty just yet. This can escalate to lock-up situation described in
previous patch.
To work-around this issue we keep track of last submit sequence number
for each ring and compare it with one written to memptrs from GPU during
execution of CACHE_FLUSH_TS event.

Fixes: b1fc2839d2 ("drm/msm: Implement preemption for A5XX targets")
Signed-off-by: Vladimir Lypak <vladimir.lypak@gmail.com>
Patchwork: https://patchwork.freedesktop.org/patch/612047/
Signed-off-by: Rob Clark <robdclark@chromium.org>
This commit is contained in:
Vladimir Lypak 2024-09-01 13:54:03 +00:00 committed by Rob Clark
parent ce050f307a
commit a30f9f65b5
3 changed files with 9 additions and 0 deletions
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4
drivers/gpu/drm/msm/adreno/a5xx_gpu.c
View File

@ -65,6 +65,8 @@ void a5xx_flush(struct msm_gpu *gpu, struct msm_ringbuffer *ring,
static void a5xx_submit_in_rb(struct msm_gpu *gpu, struct msm_gem_submit *submit)
{
struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
struct a5xx_gpu *a5xx_gpu = to_a5xx_gpu(adreno_gpu);
struct msm_ringbuffer *ring = submit->ring;
struct drm_gem_object *obj;
uint32_t *ptr, dwords;
@ -109,6 +111,7 @@ static void a5xx_submit_in_rb(struct msm_gpu *gpu, struct msm_gem_submit *submit
}
}
a5xx_gpu->last_seqno[ring->id] = submit->seqno;
a5xx_flush(gpu, ring, true);
a5xx_preempt_trigger(gpu);
@ -210,6 +213,7 @@ static void a5xx_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
/* Write the fence to the scratch register */
OUT_PKT4(ring, REG_A5XX_CP_SCRATCH_REG(2), 1);
OUT_RING(ring, submit->seqno);
a5xx_gpu->last_seqno[ring->id] = submit->seqno;
/*
* Execute a CACHE_FLUSH_TS event. This will ensure that the

1
drivers/gpu/drm/msm/adreno/a5xx_gpu.h
View File

@ -34,6 +34,7 @@ struct a5xx_gpu {
struct drm_gem_object *preempt_counters_bo[MSM_GPU_MAX_RINGS];
struct a5xx_preempt_record *preempt[MSM_GPU_MAX_RINGS];
uint64_t preempt_iova[MSM_GPU_MAX_RINGS];
uint32_t last_seqno[MSM_GPU_MAX_RINGS];
atomic_t preempt_state;
spinlock_t preempt_start_lock;

4
drivers/gpu/drm/msm/adreno/a5xx_preempt.c
View File

@ -55,6 +55,8 @@ static inline void update_wptr(struct msm_gpu *gpu, struct msm_ringbuffer *ring)
/* Return the highest priority ringbuffer with something in it */
static struct msm_ringbuffer *get_next_ring(struct msm_gpu *gpu)
{
struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
struct a5xx_gpu *a5xx_gpu = to_a5xx_gpu(adreno_gpu);
unsigned long flags;
int i;
@ -64,6 +66,8 @@ static struct msm_ringbuffer *get_next_ring(struct msm_gpu *gpu)
spin_lock_irqsave(&ring->preempt_lock, flags);
empty = (get_wptr(ring) == gpu->funcs->get_rptr(gpu, ring));
if (!empty && ring == a5xx_gpu->cur_ring)
empty = ring->memptrs->fence == a5xx_gpu->last_seqno[i];
spin_unlock_irqrestore(&ring->preempt_lock, flags);
if (!empty)