[PATCH 1/1] drm/amdgpu: Read clock counter via MMIO to reduce delay (v4)

[YuBiao Wang]

[Why]
GPU timing counters are read via KIQ under sriov, which will introduce
a delay.

[How]
It could be directly read by MMIO.

v2: Add additional check to prevent carryover issue.
v3: Only check for carryover for once to prevent performance issue.
v4: Add comments of the rough frequency where carryover happens.

Signed-off-by: YuBiao Wang <yubiao.w...@amd.com>
Acked-by: Horace Chen <horace.c...@amd.com>
---
 drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c 
b/drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c
index ff7e9f49040e..9355494002a1 100644
--- a/drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c
@@ -7609,7 +7609,7 @@ static int gfx_v10_0_soft_reset(void *handle)
 
 static uint64_t gfx_v10_0_get_gpu_clock_counter(struct amdgpu_device *adev)
 {
-       uint64_t clock;
+       uint64_t clock, clock_lo, clock_hi, hi_check;
 
        amdgpu_gfx_off_ctrl(adev, false);
        mutex_lock(&adev->gfx.gpu_clock_mutex);
@@ -7620,8 +7620,15 @@ static uint64_t gfx_v10_0_get_gpu_clock_counter(struct 
amdgpu_device *adev)
                        ((uint64_t)RREG32_SOC15(SMUIO, 0, 
mmGOLDEN_TSC_COUNT_UPPER_Vangogh) << 32ULL);
                break;
        default:
-               clock = (uint64_t)RREG32_SOC15(SMUIO, 0, 
mmGOLDEN_TSC_COUNT_LOWER) |
-                       ((uint64_t)RREG32_SOC15(SMUIO, 0, 
mmGOLDEN_TSC_COUNT_UPPER) << 32ULL);
+               clock_hi = RREG32_SOC15_NO_KIQ(SMUIO, 0, 
mmGOLDEN_TSC_COUNT_UPPER);
+               clock_lo = RREG32_SOC15_NO_KIQ(SMUIO, 0, 
mmGOLDEN_TSC_COUNT_LOWER);
+               hi_check = RREG32_SOC15_NO_KIQ(SMUIO, 0, 
mmGOLDEN_TSC_COUNT_UPPER);
+               /* Carryover happens every 4 Giga time cycles counts which is 
roughly 42 secs */
+               if (hi_check != clock_hi) {
+                       clock_lo = RREG32_SOC15_NO_KIQ(SMUIO, 0, 
mmGOLDEN_TSC_COUNT_LOWER);
+                       clock_hi = hi_check;
+               }
+               clock = (uint64_t)clock_lo | ((uint64_t)clock_hi << 32ULL);
                break;
        }
        mutex_unlock(&adev->gfx.gpu_clock_mutex);
-- 
2.25.1

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