Subject: Re: [PATCH 2/2] drm/panfrost: Use coherent pagetable walk on Juno

From: Steven Price <[email-masked]>
Date: Mon, 30 Sep 2019 17:26:27 +0100

On 30/09/2019 16:24, Robin Murphy wrote:
> Although going full "dma-coherent" ends badly due to GEM objects still
> being forcibly mapped non-cacheable, we can at least take advantage of
> Juno's ACE-lite integration to skip cache maintenance for pagetables.
> 
> CC: Rob Herring <[email-masked]>
> CC: Tomeu Vizoso <[email-masked]>
> Signed-off-by: Robin Murphy <[email-masked]>
> ---
> 
> This isn't really meant as a series, I'm just sending it together
> with patch #1 for context.
> 
>  drivers/gpu/drm/panfrost/panfrost_mmu.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> index bdd990568476..560439f63277 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> @@ -365,6 +365,9 @@ int panfrost_mmu_pgtable_alloc(struct panfrost_file_priv *priv)
>  		.iommu_dev	= pfdev->dev,
>  	};
>  
> +	if (of_device_is_compatible(pfdev->dev->of_node, "arm,juno-mali"))
> +		pfdev->mmu->pgtbl_cfg.coherent_walk = true;

Should be:
	mmu->pgtbl_cfg.coherent_walk = true;

Also I'm not sure whether we should do this based on a compatible
string. kbase has a "system-coherency" device-tree flag for it. In
theory we could end up with a long list of compatibles here...

Steve

> +
>  	mmu->pgtbl_ops = alloc_io_pgtable_ops(ARM_MALI_LPAE, &mmu->pgtbl_cfg,
>  					      priv);
>  	if (!mmu->pgtbl_ops)
> 

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