Re: [RFC] drm/msm/a6xx: Serialize GMU communication

[Dmitry Baryshkov <dmitry.baryshkov@linaro.org>]

On 27/09/2021 21:03, Rob Clark wrote:
> From: Rob Clark <robdclark@chromium.org>
> 
> I've seen some crashes in our crash reporting that *look* like multiple
> threads stomping on each other while communicating with GMU.  So wrap
> all those paths in a lock.
> 
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> ---
> Are we allowed to use c99/gnu99 yet?
> 
>   drivers/gpu/drm/msm/Makefile          |  2 +-
>   drivers/gpu/drm/msm/adreno/a6xx_gmu.c |  6 ++++
>   drivers/gpu/drm/msm/adreno/a6xx_gmu.h |  9 +++++
>   drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 50 ++++++++++++++++++++-------
>   4 files changed, 54 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/Makefile b/drivers/gpu/drm/msm/Makefile
> index 904535eda0c4..57283bbad3f0 100644
> --- a/drivers/gpu/drm/msm/Makefile
> +++ b/drivers/gpu/drm/msm/Makefile
> @@ -1,5 +1,5 @@
>   # SPDX-License-Identifier: GPL-2.0
> -ccflags-y := -I $(srctree)/$(src)
> +ccflags-y := -I $(srctree)/$(src) -std=gnu99
>   ccflags-y += -I $(srctree)/$(src)/disp/dpu1
>   ccflags-$(CONFIG_DRM_MSM_DSI) += -I $(srctree)/$(src)/dsi
>   ccflags-$(CONFIG_DRM_MSM_DP) += -I $(srctree)/$(src)/dp
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> index a7c58018959f..8b73f70766a4 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> @@ -296,6 +296,8 @@ int a6xx_gmu_set_oob(struct a6xx_gmu *gmu, enum a6xx_gmu_oob_state state)
>   	u32 val;
>   	int request, ack;
>   
> +	WARN_ON_ONCE(!mutex_is_locked(&gmu->lock));
> +
>   	if (state >= ARRAY_SIZE(a6xx_gmu_oob_bits))
>   		return -EINVAL;
>   
> @@ -337,6 +339,8 @@ void a6xx_gmu_clear_oob(struct a6xx_gmu *gmu, enum a6xx_gmu_oob_state state)
>   {
>   	int bit;
>   
> +	WARN_ON_ONCE(!mutex_is_locked(&gmu->lock));
> +
>   	if (state >= ARRAY_SIZE(a6xx_gmu_oob_bits))
>   		return;
>   
> @@ -1482,6 +1486,8 @@ int a6xx_gmu_init(struct a6xx_gpu *a6xx_gpu, struct device_node *node)
>   	if (!pdev)
>   		return -ENODEV;
>   
> +	mutex_init(&gmu->lock);
> +
>   	gmu->dev = &pdev->dev;
>   
>   	of_dma_configure(gmu->dev, node, true);
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gmu.h b/drivers/gpu/drm/msm/adreno/a6xx_gmu.h
> index 3c74f64e3126..f05a00c0afd0 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gmu.h
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gmu.h
> @@ -44,6 +44,9 @@ struct a6xx_gmu_bo {
>   struct a6xx_gmu {
>   	struct device *dev;
>   
> +	/* For serializing communication with the GMU: */
> +	struct mutex lock;
> +
>   	struct msm_gem_address_space *aspace;
>   
>   	void * __iomem mmio;
> @@ -88,6 +91,12 @@ struct a6xx_gmu {
>   	bool legacy; /* a618 or a630 */
>   };
>   
> +/* Helper macro for serializing GMU access: */
> +#define with_gmu_lock(gmu) \
> +	for (bool done = ({ mutex_lock(&(gmu)->lock); false; }); \
> +		!done; \
> +		done = ({ mutex_unlock(&(gmu)->lock); true; }))

The intent is good, but I'm not sure this kind of syntax sugar would be 
a good approach. What about calling lock/unlock explicitly, like we 
typically do? Then we won't have to use c99.

> +
>   static inline u32 gmu_read(struct a6xx_gmu *gmu, u32 offset)
>   {
>   	return msm_readl(gmu->mmio + (offset << 2));
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> index f6a4dbef796b..5e1ae3df42ba 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> @@ -881,7 +881,7 @@ static int a6xx_zap_shader_init(struct msm_gpu *gpu)
>   	  A6XX_RBBM_INT_0_MASK_UCHE_OOB_ACCESS | \
>   	  A6XX_RBBM_INT_0_MASK_UCHE_TRAP_INTR)
>   
> -static int a6xx_hw_init(struct msm_gpu *gpu)
> +static int hw_init(struct msm_gpu *gpu)
>   {
>   	struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
>   	struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> @@ -1135,6 +1135,19 @@ static int a6xx_hw_init(struct msm_gpu *gpu)
>   	return ret;
>   }
>   
> +static int a6xx_hw_init(struct msm_gpu *gpu)
> +{
> +	struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> +	struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> +	int ret;
> +
> +	with_gmu_lock(&a6xx_gpu->gmu) {
> +		ret = hw_init(gpu);
> +	}
> +
> +	return ret;
> +}
> +
>   static void a6xx_dump(struct msm_gpu *gpu)
>   {
>   	DRM_DEV_INFO(&gpu->pdev->dev, "status:   %08x\n",
> @@ -1509,7 +1522,9 @@ static int a6xx_pm_resume(struct msm_gpu *gpu)
>   
>   	trace_msm_gpu_resume(0);
>   
> -	ret = a6xx_gmu_resume(a6xx_gpu);
> +	with_gmu_lock(&a6xx_gpu->gmu) {
> +		ret = a6xx_gmu_resume(a6xx_gpu);
> +	}
>   	if (ret)
>   		return ret;
>   
> @@ -1532,7 +1547,9 @@ static int a6xx_pm_suspend(struct msm_gpu *gpu)
>   
>   	msm_devfreq_suspend(gpu);
>   
> -	ret = a6xx_gmu_stop(a6xx_gpu);
> +	with_gmu_lock(&a6xx_gpu->gmu) {
> +		ret = a6xx_gmu_stop(a6xx_gpu);
> +	}
>   	if (ret)
>   		return ret;
>   
> @@ -1547,18 +1564,17 @@ static int a6xx_get_timestamp(struct msm_gpu *gpu, uint64_t *value)
>   {
>   	struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
>   	struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> -	static DEFINE_MUTEX(perfcounter_oob);
>   
> -	mutex_lock(&perfcounter_oob);
> +	with_gmu_lock(&a6xx_gpu->gmu) {
> +		/* Force the GPU power on so we can read this register */
> +		a6xx_gmu_set_oob(&a6xx_gpu->gmu, GMU_OOB_PERFCOUNTER_SET);
>   
> -	/* Force the GPU power on so we can read this register */
> -	a6xx_gmu_set_oob(&a6xx_gpu->gmu, GMU_OOB_PERFCOUNTER_SET);
> +		*value = gpu_read64(gpu, REG_A6XX_CP_ALWAYS_ON_COUNTER_LO,
> +				    REG_A6XX_CP_ALWAYS_ON_COUNTER_HI);
>   
> -	*value = gpu_read64(gpu, REG_A6XX_CP_ALWAYS_ON_COUNTER_LO,
> -		REG_A6XX_CP_ALWAYS_ON_COUNTER_HI);
> +		a6xx_gmu_clear_oob(&a6xx_gpu->gmu, GMU_OOB_PERFCOUNTER_SET);
> +	}
>   
> -	a6xx_gmu_clear_oob(&a6xx_gpu->gmu, GMU_OOB_PERFCOUNTER_SET);
> -	mutex_unlock(&perfcounter_oob);
>   	return 0;
>   }
>   
> @@ -1622,6 +1638,16 @@ static unsigned long a6xx_gpu_busy(struct msm_gpu *gpu)
>   	return (unsigned long)busy_time;
>   }
>   
> +void a6xx_gpu_set_freq(struct msm_gpu *gpu, struct dev_pm_opp *opp)
> +{
> +	struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> +	struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> +
> +	with_gmu_lock(&a6xx_gpu->gmu) {
> +		a6xx_gmu_set_freq(gpu, opp);
> +	}
> +}
> +
>   static struct msm_gem_address_space *
>   a6xx_create_address_space(struct msm_gpu *gpu, struct platform_device *pdev)
>   {
> @@ -1766,7 +1792,7 @@ static const struct adreno_gpu_funcs funcs = {
>   #endif
>   		.gpu_busy = a6xx_gpu_busy,
>   		.gpu_get_freq = a6xx_gmu_get_freq,
> -		.gpu_set_freq = a6xx_gmu_set_freq,
> +		.gpu_set_freq = a6xx_gpu_set_freq,
>   #if defined(CONFIG_DRM_MSM_GPU_STATE)
>   		.gpu_state_get = a6xx_gpu_state_get,
>   		.gpu_state_put = a6xx_gpu_state_put,
> 


-- 
With best wishes
Dmitry