[PATCH] drm/amdgpu: Make KIQ read/write register routine be atomic

[Shaoyun Liu]

1. Use spin lock instead of mutex in KIQ
2. Directly write to KIQ fence address instead of using fence_emit()
3. Disable the interrupt for KIQ read/write and use CPU polling

Change-Id: Id3693a2878ce1338f55aee3def6e7fc0f6b81996
Signed-off-by: Shaoyun Liu <Shaoyun.Liu at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu.h      |  2 +-
 drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c  |  2 +-
 drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c | 57 ++++++++++++++++++++++----------
 3 files changed, 41 insertions(+), 20 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
index ab1dad2..a155206 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
@@ -955,7 +955,7 @@ struct amdgpu_mec {
 struct amdgpu_kiq {
 	u64			eop_gpu_addr;
 	struct amdgpu_bo	*eop_obj;
-	struct mutex		ring_mutex;
+	spinlock_t		ring_lock;
 	struct amdgpu_ring	ring;
 	struct amdgpu_irq_src	irq;
 };
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
index e26108a..e5e5541 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
@@ -184,7 +184,7 @@ int amdgpu_gfx_kiq_init_ring(struct amdgpu_device *adev,
 	struct amdgpu_kiq *kiq = &adev->gfx.kiq;
 	int r = 0;
 
-	mutex_init(&kiq->ring_mutex);
+	spin_lock_init(&kiq->ring_lock);
 
 	r = amdgpu_wb_get(adev, &adev->virt.reg_val_offs);
 	if (r)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
index 8a081e1..95b4975 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
@@ -116,24 +116,33 @@ uint32_t amdgpu_virt_kiq_rreg(struct amdgpu_device *adev, uint32_t reg)
 {
 	signed long r;
 	uint32_t val;
-	struct dma_fence *f;
 	struct amdgpu_kiq *kiq = &adev->gfx.kiq;
 	struct amdgpu_ring *ring = &kiq->ring;
+	unsigned long end_jiffies;
+	uint32_t seq;
+	volatile uint32_t *f;
 
 	BUG_ON(!ring->funcs->emit_rreg);
 
-	mutex_lock(&kiq->ring_mutex);
+	spin_lock(&kiq->ring_lock);
 	amdgpu_ring_alloc(ring, 32);
 	amdgpu_ring_emit_rreg(ring, reg);
-	amdgpu_fence_emit(ring, &f);
+	f = ring->fence_drv.cpu_addr;
+	*f = 0;
+	seq = ++ring->fence_drv.sync_seq;
+	amdgpu_ring_emit_fence(ring, ring->fence_drv.gpu_addr, seq, 0);
 	amdgpu_ring_commit(ring);
-	mutex_unlock(&kiq->ring_mutex);
-
-	r = dma_fence_wait_timeout(f, false, msecs_to_jiffies(MAX_KIQ_REG_WAIT));
-	dma_fence_put(f);
-	if (r < 1) {
-		DRM_ERROR("wait for kiq fence error: %ld.\n", r);
-		return ~0;
+	spin_unlock(&kiq->ring_lock);
+
+	end_jiffies = (MAX_KIQ_REG_WAIT * HZ / 1000) + jiffies;
+	while (true) {
+		if (*f >= seq)
+			break;
+		if (time_after(jiffies, end_jiffies)) {
+			DRM_ERROR("wait for kiq fence error: %ld.\n", r);
+			return ~0;
+		}
+		cpu_relax();
 	}
 
 	val = adev->wb.wb[adev->virt.reg_val_offs];
@@ -144,23 +153,35 @@ uint32_t amdgpu_virt_kiq_rreg(struct amdgpu_device *adev, uint32_t reg)
 void amdgpu_virt_kiq_wreg(struct amdgpu_device *adev, uint32_t reg, uint32_t v)
 {
 	signed long r;
-	struct dma_fence *f;
 	struct amdgpu_kiq *kiq = &adev->gfx.kiq;
 	struct amdgpu_ring *ring = &kiq->ring;
+	unsigned long end_jiffies;
+	uint32_t seq;
+	volatile uint32_t *f;
 
 	BUG_ON(!ring->funcs->emit_wreg);
 
-	mutex_lock(&kiq->ring_mutex);
+	spin_lock(&kiq->ring_lock);
 	amdgpu_ring_alloc(ring, 32);
 	amdgpu_ring_emit_wreg(ring, reg, v);
-	amdgpu_fence_emit(ring, &f);
+	f = ring->fence_drv.cpu_addr;
+	*f = 0;
+	seq = ++ring->fence_drv.sync_seq;
+	amdgpu_ring_emit_fence(ring, ring->fence_drv.gpu_addr, seq, 0);
 	amdgpu_ring_commit(ring);
-	mutex_unlock(&kiq->ring_mutex);
+	spin_unlock(&kiq->ring_lock);
+
+	end_jiffies = (MAX_KIQ_REG_WAIT * HZ / 1000) + jiffies;
+	while (true) {
+		if (*f >= seq)
+			break;
+		if (time_after(jiffies, end_jiffies)) {
+			DRM_ERROR("wait for kiq fence error: %ld.\n", r);
+			return;
+		}
+		cpu_relax();
+	}
 
-	r = dma_fence_wait_timeout(f, false, msecs_to_jiffies(MAX_KIQ_REG_WAIT));
-	if (r < 1)
-		DRM_ERROR("wait for kiq fence error: %ld.\n", r);
-	dma_fence_put(f);
 }
 
 /**
-- 
1.9.1