Re: [PATCH 2/3] drm/panfrost: Support cache-coherent integrations

[Steven Price <steven.price@arm.com>]

On 16/09/2020 00:51, Robin Murphy wrote:
> When the GPU's ACE-Lite interface is fully wired up and capable of
> snooping CPU caches, it may be described as "dma-coherent" in
> devicetree, which will already inform the DMA layer not to perform
> unnecessary cache maintenance. However, we still need to ensure that
> the GPU uses the appropriate cacheable outer-shareable attributes in
> order to generate the requisite snoop signals, and that CPU mappings
> don't create a mismatch by using a non-cacheable type either.
> 
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>

LGTM

Reviewed-by: Steven Price <steven.price@arm.com>

> ---
>   drivers/gpu/drm/panfrost/panfrost_device.h | 1 +
>   drivers/gpu/drm/panfrost/panfrost_drv.c    | 2 ++
>   drivers/gpu/drm/panfrost/panfrost_gem.c    | 2 ++
>   drivers/gpu/drm/panfrost/panfrost_mmu.c    | 1 +
>   4 files changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
> index c30c719a8059..b31f45315e96 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
> @@ -84,6 +84,7 @@ struct panfrost_device {
>   	/* pm_domains for devices with more than one. */
>   	struct device *pm_domain_devs[MAX_PM_DOMAINS];
>   	struct device_link *pm_domain_links[MAX_PM_DOMAINS];
> +	bool coherent;
>   
>   	struct panfrost_features features;
>   	const struct panfrost_compatible *comp;
> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> index ada51df9a7a3..2a6f2f716b2f 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> @@ -588,6 +588,8 @@ static int panfrost_probe(struct platform_device *pdev)
>   	if (!pfdev->comp)
>   		return -ENODEV;
>   
> +	pfdev->coherent = device_get_dma_attr(&pdev->dev) == DEV_DMA_COHERENT;
> +
>   	/* Allocate and initialze the DRM device. */
>   	ddev = drm_dev_alloc(&panfrost_drm_driver, &pdev->dev);
>   	if (IS_ERR(ddev))
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
> index 33355dd302f1..cdf1a8754eba 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
> @@ -220,6 +220,7 @@ static const struct drm_gem_object_funcs panfrost_gem_funcs = {
>    */
>   struct drm_gem_object *panfrost_gem_create_object(struct drm_device *dev, size_t size)
>   {
> +	struct panfrost_device *pfdev = dev->dev_private;
>   	struct panfrost_gem_object *obj;
>   
>   	obj = kzalloc(sizeof(*obj), GFP_KERNEL);
> @@ -229,6 +230,7 @@ struct drm_gem_object *panfrost_gem_create_object(struct drm_device *dev, size_t
>   	INIT_LIST_HEAD(&obj->mappings.list);
>   	mutex_init(&obj->mappings.lock);
>   	obj->base.base.funcs = &panfrost_gem_funcs;
> +	obj->base.map_cached = pfdev->coherent;
>   
>   	return &obj->base.base;
>   }
> diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> index e8f7b11352d2..8852fd378f7a 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> @@ -371,6 +371,7 @@ int panfrost_mmu_pgtable_alloc(struct panfrost_file_priv *priv)
>   		.pgsize_bitmap	= SZ_4K | SZ_2M,
>   		.ias		= FIELD_GET(0xff, pfdev->features.mmu_features),
>   		.oas		= FIELD_GET(0xff00, pfdev->features.mmu_features),
> +		.coherent_walk	= pfdev->coherent,
>   		.tlb		= &mmu_tlb_ops,
>   		.iommu_dev	= pfdev->dev,
>   	};
> 

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