Re: [RFC PATCH 3/4] drm/panfrost: Support ARM_64_LPAE_S1 page table

[Ariel D'Alessandro]

Boris,

On 2/27/25 5:30 AM, Boris Brezillon wrote:
> On Wed, 26 Feb 2025 15:30:42 -0300
> Ariel D'Alessandro <ariel.dalessandro@xxxxxxxxxxxxx> wrote:
>
> > Bifrost MMUs support AArch64 4kB granule specification. However,
> > panfrost only enables MMU in legacy mode, despite the presence of the
> > HW_FEATURE_AARCH64_MMU feature flag.
> >
> > This commit adds support to use page tables according to AArch64 4kB
> > granule specification. This feature is enabled conditionally based on
> > the GPU model's HW_FEATURE_AARCH64_MMU feature flag.
> >
> > Signed-off-by: Ariel D'Alessandro <ariel.dalessandro@xxxxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/panfrost/panfrost_device.h |   1 +
> >   drivers/gpu/drm/panfrost/panfrost_mmu.c    | 118 +++++++++++++++++----
> >   drivers/gpu/drm/panfrost/panfrost_regs.h   |  29 +++++
> >   3 files changed, 128 insertions(+), 20 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
> > index cffcb0ac7c11..dea252f43c58 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_device.h
> > +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
> > @@ -153,6 +153,7 @@ struct panfrost_device {
> >   };
> >   
> >   struct panfrost_mmu {
> > +	void (*enable)(struct panfrost_device *pfdev, struct panfrost_mmu *mmu);
>
> The enable sequence is the same, it's just the transtab, memattr and
> transcfg values that differ depending on the format, so let's prepare
> them at panfrost_mmu init time, and cache them here.

Agreed. AFAICS, this would be:

Add the following to struct panfrost_mmu:

struct {
	u64 transtab;
	u64 memattr;
	u64 transcfg;
} cfg;

and have it initialized in panfrost_mmu_ctx_create().

For consistency, we should do this for both modes MALI_LPAE and 
AARCH64_4K. As for the MALI_LPAE case, I'd move out the initialization 
done in drivers/iommu/io-pgtable-arm.c for:

struct {
	u64     transtab;
	u64     memattr;
} arm_mali_lpae_cfg;

I'll send a proposal for this in the next patchset v1.

Thanks!

--
Ariel D'Alessandro
Software Engineer

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