drm/amdgpu: busywait KIQ register accessing (v4)

Register accessing is performed when IRQ is disabled. Never sleep in
this function.

Known issue: dead sleep in many use cases of index/data registers.

v2:
 - wrap polling fence functions.
 - don't trigger IRQ for polling in case of wrongly fence signal.

v3:
 - handle wrap round gracefully.
 - add comments for polling function

v4:
 - don't return negative timeout confused with error code

Signed-off-by: pding <Pixel.Ding@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu.h

@@ -879,7 +879,7 @@ 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;
 };

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c

@@ -109,10 +109,8 @@ uint32_t amdgpu_mm_rreg(struct amdgpu_device *adev, uint32_t reg,
 {
 	uint32_t ret;
 
-	if (!(acc_flags & AMDGPU_REGS_NO_KIQ) && amdgpu_sriov_runtime(adev)) {
-		BUG_ON(in_interrupt());
+	if (!(acc_flags & AMDGPU_REGS_NO_KIQ) && amdgpu_sriov_runtime(adev))
 		return amdgpu_virt_kiq_rreg(adev, reg);
-	}
 
 	if ((reg * 4) < adev->rmmio_size && !(acc_flags & AMDGPU_REGS_IDX))
 		ret = readl(((void __iomem *)adev->rmmio) + (reg * 4));
@@ -137,10 +135,8 @@ void amdgpu_mm_wreg(struct amdgpu_device *adev, uint32_t reg, uint32_t v,
 		adev->last_mm_index = v;
 	}
 
-	if (!(acc_flags & AMDGPU_REGS_NO_KIQ) && amdgpu_sriov_runtime(adev)) {
-		BUG_ON(in_interrupt());
+	if (!(acc_flags & AMDGPU_REGS_NO_KIQ) && amdgpu_sriov_runtime(adev))
 		return amdgpu_virt_kiq_wreg(adev, reg, v);
-	}
 
 	if ((reg * 4) < adev->rmmio_size && !(acc_flags & AMDGPU_REGS_IDX))
 		writel(v, ((void __iomem *)adev->rmmio) + (reg * 4));

drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c

@@ -168,6 +168,32 @@ int amdgpu_fence_emit(struct amdgpu_ring *ring, struct dma_fence **f)
 	return 0;
 }
 
+/**
+ * amdgpu_fence_emit_polling - emit a fence on the requeste ring
+ *
+ * @ring: ring the fence is associated with
+ * @s: resulting sequence number
+ *
+ * Emits a fence command on the requested ring (all asics).
+ * Used For polling fence.
+ * Returns 0 on success, -ENOMEM on failure.
+ */
+int amdgpu_fence_emit_polling(struct amdgpu_ring *ring, uint32_t *s)
+{
+	uint32_t seq;
+
+	if (!s)
+		return -EINVAL;
+
+	seq = ++ring->fence_drv.sync_seq;
+	amdgpu_ring_emit_fence(ring, ring->fence_drv.gpu_addr,
+			       seq, AMDGPU_FENCE_FLAG_INT);
+
+	*s = seq;
+
+	return 0;
+}
+
 /**
  * amdgpu_fence_schedule_fallback - schedule fallback check
  *
@@ -281,6 +307,30 @@ int amdgpu_fence_wait_empty(struct amdgpu_ring *ring)
 	return r;
 }
 
+/**
+ * amdgpu_fence_wait_polling - busy wait for givn sequence number
+ *
+ * @ring: ring index the fence is associated with
+ * @wait_seq: sequence number to wait
+ * @timeout: the timeout for waiting in usecs
+ *
+ * Wait for all fences on the requested ring to signal (all asics).
+ * Returns left time if no timeout, 0 or minus if timeout.
+ */
+signed long amdgpu_fence_wait_polling(struct amdgpu_ring *ring,
+				      uint32_t wait_seq,
+				      signed long timeout)
+{
+	uint32_t seq;
+
+	do {
+		seq = amdgpu_fence_read(ring);
+		udelay(5);
+		timeout -= 5;
+	} while ((int32_t)(wait_seq - seq) > 0 && timeout > 0);
+
+	return timeout > 0 ? timeout : 0;
+}
 /**
  * amdgpu_fence_count_emitted - get the count of emitted fences
  *

drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c

@@ -201,7 +201,7 @@ 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)

drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h

@@ -90,8 +90,12 @@ int amdgpu_fence_driver_start_ring(struct amdgpu_ring *ring,
 void amdgpu_fence_driver_suspend(struct amdgpu_device *adev);
 void amdgpu_fence_driver_resume(struct amdgpu_device *adev);
 int amdgpu_fence_emit(struct amdgpu_ring *ring, struct dma_fence **fence);
+int amdgpu_fence_emit_polling(struct amdgpu_ring *ring, uint32_t *s);
 void amdgpu_fence_process(struct amdgpu_ring *ring);
 int amdgpu_fence_wait_empty(struct amdgpu_ring *ring);
+signed long amdgpu_fence_wait_polling(struct amdgpu_ring *ring,
+				      uint32_t wait_seq,
+				      signed long timeout);
 unsigned amdgpu_fence_count_emitted(struct amdgpu_ring *ring);
 
 /*

drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c

@@ -22,7 +22,7 @@
  */
 
 #include "amdgpu.h"
-#define MAX_KIQ_REG_WAIT	100000
+#define MAX_KIQ_REG_WAIT	100000000 /* in usecs */
 
 int amdgpu_allocate_static_csa(struct amdgpu_device *adev)
 {
@@ -114,27 +114,24 @@ void amdgpu_virt_init_setting(struct amdgpu_device *adev)
 uint32_t amdgpu_virt_kiq_rreg(struct amdgpu_device *adev, uint32_t reg)
 {
 	signed long r;
-	uint32_t val;
-	struct dma_fence *f;
+	uint32_t val, seq;
 	struct amdgpu_kiq *kiq = &adev->gfx.kiq;
 	struct amdgpu_ring *ring = &kiq->ring;
 
 	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);
+	amdgpu_fence_emit_polling(ring, &seq);
 	amdgpu_ring_commit(ring);
-	mutex_unlock(&kiq->ring_mutex);
+	spin_unlock(&kiq->ring_lock);
 
-	r = dma_fence_wait_timeout(f, false, msecs_to_jiffies(MAX_KIQ_REG_WAIT));
-	dma_fence_put(f);
+	r = amdgpu_fence_wait_polling(ring, seq, MAX_KIQ_REG_WAIT);
 	if (r < 1) {
-		DRM_ERROR("wait for kiq fence error: %ld.\n", r);
+		DRM_ERROR("wait for kiq fence error: %ld\n", r);
 		return ~0;
 	}
-
 	val = adev->wb.wb[adev->virt.reg_val_offs];
 
 	return val;
@@ -143,23 +140,22 @@ 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;
+	uint32_t seq;
 	struct amdgpu_kiq *kiq = &adev->gfx.kiq;
 	struct amdgpu_ring *ring = &kiq->ring;
 
 	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);
+	amdgpu_fence_emit_polling(ring, &seq);
 	amdgpu_ring_commit(ring);
-	mutex_unlock(&kiq->ring_mutex);
+	spin_unlock(&kiq->ring_lock);
 
-	r = dma_fence_wait_timeout(f, false, msecs_to_jiffies(MAX_KIQ_REG_WAIT));
+	r = amdgpu_fence_wait_polling(ring, seq, MAX_KIQ_REG_WAIT);
 	if (r < 1)
-		DRM_ERROR("wait for kiq fence error: %ld.\n", r);
-	dma_fence_put(f);
+		DRM_ERROR("wait for kiq fence error: %ld\n", r);
 }
 
 /**