[PATCH] drm/panfrost: Add PANFROST_BO_NO{READ,WRITE} flags

[Boris Brezillon]

Hi Robin,

On Thu, 30 Sep 2021 21:44:24 +0200
Boris Brezillon <boris.brezillon at collabora.com> wrote:

> On Thu, 30 Sep 2021 20:47:23 +0200
> Boris Brezillon <boris.brezillon at collabora.com> wrote:
> 
> > So we can create GPU mappings without R/W permissions. Particularly
> > useful to debug corruptions caused by out-of-bound writes.  
> 
> Oops, I forgot to add the PANFROST_BO_PRIVATE flag suggested by Robin
> here [1]. I'll send a v2.

When you're talking about a PANFROST_BO_GPU_PRIVATE flag (or
PANFROST_BO_NO_CPU_ACCESS), you mean something that can set
ARM_LPAE_PTE_SH_IS instead of the unconditional ARM_LPAE_PTE_SH_OS we
have right now [1], right? In this case, how would you pass this info
to the iommu? Looks like we have an IOMMU_CACHE, but I don't think
it reflects what we're trying to do. IOMMU_PRIV is about privileged
mappings, so definitely not what we want. Should we add a new
IOMMU_NO_{EXTERNAL,HOST,CPU}_ACCESS flag for that?

Regards,

Boris

[1]https://elixir.bootlin.com/linux/v5.15-rc3/source/drivers/iommu/io-pgtable-arm.c#L453