Re: [PATCH 1/1] drm/amdgpu: Read clock counter via MMIO to reduce delay (v5)

["Lazar, Lijo" <lijo.lazar@amd.com>]

A few comments to take care of before submitting the changes.

Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>

On 7/1/2021 3:27 PM, YuBiao Wang wrote:
> [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.
> v5: Remove mutex and gfxoff ctrl unused with current timing registers.
> 
> Signed-off-by: YuBiao Wang <YuBiao.Wang@amd.com>
> Acked-by: Horace Chen <horace.chen@amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c | 19 ++++++++++++-------
>   1 file changed, 12 insertions(+), 7 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..5f4eae9c9526 100644
> --- a/drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c
> +++ b/drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c
> @@ -7609,10 +7609,8 @@ 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);
>   	switch (adev->asic_type) {
>   	case CHIP_VANGOGH:
>   	case CHIP_YELLOW_CARP:
> @@ -7620,12 +7618,19 @@ 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);
> +		/* The GFX clock frequency is 100MHz, which sets 32-bit carry over
> +		 * roughly every 42 seconds.
> +		 */

SMUIO TSC is not ticking based on GFX clock frequency, it's running at a 
fixed SMUIO TSC Clock frequency which is 100MHz (second part is right).

Replace GFX Clock with SMUIO TSC Clock.

> +		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);

These types are already uint64_t and looks cleaner without the cast.

Thanks,
Lijo

>   		break;
>   	}
> -	mutex_unlock(&adev->gfx.gpu_clock_mutex);
> -	amdgpu_gfx_off_ctrl(adev, true);
>   	return clock;
>   }
>   
> 
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