linux-kernel - Re: [PATCH 2/3] drm/msm: add DRM_MSM_GEM_SYNC_CACHE for non-coherent cache maintenance

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Date:   Fri, 2 Oct 2020 08:53:21 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Jonathan Marek <jonathan@...ek.ca>
Cc:     freedreno@...ts.freedesktop.org, Rob Clark <robdclark@...il.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <linux-arm-msm@...r.kernel.org>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <dri-devel@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] drm/msm: add DRM_MSM_GEM_SYNC_CACHE for non-coherent
 cache maintenance

> @@ -8,6 +8,7 @@
>  #include <linux/shmem_fs.h>
>  #include <linux/dma-buf.h>
>  #include <linux/pfn_t.h>
> +#include <linux/dma-noncoherent.h>

NAK, dma-noncoherent.h is not for driver use.  And will in fact go
away in 5.10.

>  
>  #include <drm/drm_prime.h>
>  
> @@ -808,6 +809,20 @@ int msm_gem_cpu_fini(struct drm_gem_object *obj)
>  	return 0;
>  }
>  
> +void msm_gem_sync_cache(struct drm_gem_object *obj, uint32_t flags,
> +		size_t range_start, size_t range_end)
> +{
> +	struct msm_gem_object *msm_obj = to_msm_bo(obj);
> +
> +	/* TODO: sync only the required range, and don't invalidate on clean */
> +
> +	if (flags & MSM_GEM_SYNC_CACHE_CLEAN)
> +		sync_for_device(msm_obj);
> +
> +	if (flags & MSM_GEM_SYNC_CACHE_INVALIDATE)
> +		sync_for_cpu(msm_obj);

And make to these ones as well.  They are complete abuses of the DMA
API, and while we had to live with that for now to not cause regressions
they absoutely must not be exposed in a userspace ABI like this.