Re: [PATCH v3 4/8] drm/etnaviv: replace MMU flush marker with flush sequence

["Guido Günther" <agx@sigxcpu.org>]

Hi,
On Fri, Aug 09, 2019 at 02:04:20PM +0200, Lucas Stach wrote:
> If a MMU is shared between multiple GPUs, all of them need to flush their
> TLBs, so a single marker that gets reset on the first flush won't do.
> Replace the flush marker with a sequence number, so that it's possible to
> check if the TLB is in sync with the current page table state for each GPU.
> 
> Signed-off-by: Lucas Stach <l.stach@pengutronix.de>

Reviewed-by: Guido Günther <agx@sigxcpu.org>

> ---
> v3: Avoid flush sequence update racing with the flush.
> ---
>  drivers/gpu/drm/etnaviv/etnaviv_buffer.c | 10 ++++++----
>  drivers/gpu/drm/etnaviv/etnaviv_gpu.h    |  1 +
>  drivers/gpu/drm/etnaviv/etnaviv_mmu.c    |  6 +++---
>  drivers/gpu/drm/etnaviv/etnaviv_mmu.h    |  2 +-
>  4 files changed, 11 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_buffer.c b/drivers/gpu/drm/etnaviv/etnaviv_buffer.c
> index 6400a88cd778..a3cdb20bfc5f 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_buffer.c
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_buffer.c
> @@ -315,6 +315,8 @@ void etnaviv_buffer_queue(struct etnaviv_gpu *gpu, u32 exec_state,
>  	u32 return_target, return_dwords;
>  	u32 link_target, link_dwords;
>  	bool switch_context = gpu->exec_state != exec_state;
> +	unsigned int new_flush_seq = READ_ONCE(gpu->mmu->flush_seq);
> +	bool need_flush = gpu->flush_seq != new_flush_seq;
>  
>  	lockdep_assert_held(&gpu->lock);
>  
> @@ -329,14 +331,14 @@ void etnaviv_buffer_queue(struct etnaviv_gpu *gpu, u32 exec_state,
>  	 * need to append a mmu flush load state, followed by a new
>  	 * link to this buffer - a total of four additional words.
>  	 */
> -	if (gpu->mmu->need_flush || switch_context) {
> +	if (need_flush || switch_context) {
>  		u32 target, extra_dwords;
>  
>  		/* link command */
>  		extra_dwords = 1;
>  
>  		/* flush command */
> -		if (gpu->mmu->need_flush) {
> +		if (need_flush) {
>  			if (gpu->mmu->version == ETNAVIV_IOMMU_V1)
>  				extra_dwords += 1;
>  			else
> @@ -349,7 +351,7 @@ void etnaviv_buffer_queue(struct etnaviv_gpu *gpu, u32 exec_state,
>  
>  		target = etnaviv_buffer_reserve(gpu, buffer, extra_dwords);
>  
> -		if (gpu->mmu->need_flush) {
> +		if (need_flush) {
>  			/* Add the MMU flush */
>  			if (gpu->mmu->version == ETNAVIV_IOMMU_V1) {
>  				CMD_LOAD_STATE(buffer, VIVS_GL_FLUSH_MMU,
> @@ -369,7 +371,7 @@ void etnaviv_buffer_queue(struct etnaviv_gpu *gpu, u32 exec_state,
>  					SYNC_RECIPIENT_PE);
>  			}
>  
> -			gpu->mmu->need_flush = false;
> +			gpu->flush_seq = new_flush_seq;
>  		}
>  
>  		if (switch_context) {
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gpu.h b/drivers/gpu/drm/etnaviv/etnaviv_gpu.h
> index 933c8d016f11..96380942cd8c 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_gpu.h
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gpu.h
> @@ -137,6 +137,7 @@ struct etnaviv_gpu {
>  	int irq;
>  
>  	struct etnaviv_iommu *mmu;
> +	unsigned int flush_seq;
>  
>  	/* Power Control: */
>  	struct clk *clk_bus;
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_mmu.c b/drivers/gpu/drm/etnaviv/etnaviv_mmu.c
> index 09f516093b91..bbd1624a3df8 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_mmu.c
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_mmu.c
> @@ -263,7 +263,7 @@ int etnaviv_iommu_map_gem(struct etnaviv_iommu *mmu,
>  	}
>  
>  	list_add_tail(&mapping->mmu_node, &mmu->mappings);
> -	mmu->need_flush = true;
> +	mmu->flush_seq++;
>  unlock:
>  	mutex_unlock(&mmu->lock);
>  
> @@ -282,7 +282,7 @@ void etnaviv_iommu_unmap_gem(struct etnaviv_iommu *mmu,
>  		etnaviv_iommu_remove_mapping(mmu, mapping);
>  
>  	list_del(&mapping->mmu_node);
> -	mmu->need_flush = true;
> +	mmu->flush_seq++;
>  	mutex_unlock(&mmu->lock);
>  }
>  
> @@ -369,7 +369,7 @@ int etnaviv_iommu_get_suballoc_va(struct etnaviv_iommu *mmu,
>  			return ret;
>  		}
>  
> -		mmu->need_flush = true;
> +		mmu->flush_seq++;
>  	}
>  
>  	list_add_tail(&mapping->mmu_node, &mmu->mappings);
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_mmu.h b/drivers/gpu/drm/etnaviv/etnaviv_mmu.h
> index fe1c9d6b9334..34afe25df9ca 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_mmu.h
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_mmu.h
> @@ -48,7 +48,7 @@ struct etnaviv_iommu {
>  	struct mutex lock;
>  	struct list_head mappings;
>  	struct drm_mm mm;
> -	bool need_flush;
> +	unsigned int flush_seq;
>  };
>  
>  struct etnaviv_gem_object;
> -- 
> 2.20.1
> 
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