Re: [PATCH 11/11] drm/msm: Implement preemption for A5XX targets

From: Stephen Boyd <sboyd-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>
To: Jordan Crouse <jcrouse-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>,
	freedreno-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org
Cc: linux-arm-msm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org
Subject: Re: [PATCH 11/11] drm/msm: Implement preemption for A5XX targets
Date: Wed, 8 Feb 2017 12:30:08 -0800	[thread overview]
Message-ID: <8696f3b7-1fbd-309a-1d68-b2f8ad89a30c@codeaurora.org> (raw)
In-Reply-To: <1486402779-9024-12-git-send-email-jcrouse-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>

On 02/06/2017 09:39 AM, Jordan Crouse wrote:
> diff --git a/drivers/gpu/drm/msm/adreno/a5xx_preempt.c b/drivers/gpu/drm/msm/adreno/a5xx_preempt.c
> new file mode 100644
> index 0000000..348ead7
> --- /dev/null
> +++ b/drivers/gpu/drm/msm/adreno/a5xx_preempt.c
> @@ -0,0 +1,367 @@
>
> +/*
> + * Try to transition the preemption state from old to new. Return
> + * true on success or false if the original state wasn't 'old'
> + */
> +static inline bool try_preempt_state(struct a5xx_gpu *a5xx_gpu,
> +		enum preempt_state old, enum preempt_state new)
> +{
> +	enum preempt_state cur = atomic_cmpxchg(&a5xx_gpu->preempt_state,
> +		old, new);
> +
> +	return (cur == old);
> +}
> +
> +/*
> + * Force the preemption state to the specified state.  This is used in cases
> + * where the current state is known and won't change
> + */
> +static inline void set_preempt_state(struct a5xx_gpu *gpu,
> +		enum preempt_state new)
> +{
> +	/* atomic_set() doesn't automatically do barriers, so one before.. */
> +	smp_wmb();
> +	atomic_set(&gpu->preempt_state, new);
> +	/* ... and one after*/
> +	smp_wmb();

Should these smp_wmb()s be replaced with smp_mb__before_atomic() and
smp_mb__after_atomic()? The latter is stronger (mb() instead of wmb())
but otherwise that's typically what is used with atomics. Also, it would
be nice if the comments described what we're synchronizing with.

> +
> +static void a5xx_preempt_worker(struct work_struct *work)
> +{
> +	struct a5xx_gpu *a5xx_gpu =
> +		container_of(work, struct a5xx_gpu, preempt_work);
> +	struct msm_gpu *gpu = &a5xx_gpu->base.base;
> +	struct drm_device *dev = gpu->dev;
> +	struct msm_drm_private *priv = dev->dev_private;
> +
> +	if (atomic_read(&a5xx_gpu->preempt_state) == PREEMPT_COMPLETE) {
> +		uint32_t status = gpu_read(gpu,
> +			REG_A5XX_CP_CONTEXT_SWITCH_CNTL);

Why does this worker check the status again? The irq may fire but the
hardware is still indicating "pending"? And why do we fork off this code
to a workqueue? Can't we do this stuff in the irq handler or timer
handler and drop this worker?

> +
> +		if (status == 0) {
> +			del_timer(&a5xx_gpu->preempt_timer);
> +			a5xx_gpu->cur_ring = a5xx_gpu->next_ring;
> +			a5xx_gpu->next_ring = NULL;
> +
> +			update_wptr(gpu, a5xx_gpu->cur_ring);
> +
> +			set_preempt_state(a5xx_gpu, PREEMPT_NONE);
> +			return;
> +		}
> +
> +		dev_err(dev->dev, "%s: Preemption failed to complete\n",
> +			gpu->name);
> +	} else if (atomic_read(&a5xx_gpu->preempt_state) == PREEMPT_FAULTED)
> +		dev_err(dev->dev, "%s: preemption timed out\n", gpu->name);
> +	else
> +		return;
> +
> +	/* Trigger recovery */
> +	queue_work(priv->wq, &gpu->recover_work);
> +}
> diff --git a/drivers/gpu/drm/msm/adreno/adreno_gpu.h b/drivers/gpu/drm/msm/adreno/adreno_gpu.h
> index f5118ad..4fcccd4 100644
> --- a/drivers/gpu/drm/msm/adreno/adreno_gpu.h
> +++ b/drivers/gpu/drm/msm/adreno/adreno_gpu.h
> @@ -334,6 +334,11 @@ static inline void adreno_gpu_write64(struct adreno_gpu *gpu,
>  	adreno_gpu_write(gpu, hi, upper_32_bits(data));
>  }
>  
> +static inline uint32_t get_wptr(struct msm_ringbuffer *ring)

const struct msm_ringbuffer?

> +{
> +	return ring->cur - ring->start;
> +}
> +
>  /*
>   * Given a register and a count, return a value to program into
>   * REG_CP_PROTECT_REG(n) - this will block both reads and writes for _len
>
-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

_______________________________________________
Freedreno mailing list
Freedreno@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/freedreno