linux-kernel - Re: [RFC PATCH 3/4] drm/panfrost: Support ARM_64_LPAE

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Message-ID: <20250310202543.404e21c0@collabora.com>
Date: Mon, 10 Mar 2025 20:25:43 +0100
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Ariel D'Alessandro <ariel.dalessandro@...labora.com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 robh@...nel.org, steven.price@....com, maarten.lankhorst@...ux.intel.com,
 mripard@...nel.org, tzimmermann@...e.de, airlied@...il.com, simona@...ll.ch
Subject: Re: [RFC PATCH 3/4] drm/panfrost: Support ARM_64_LPAE_S1 page table

On Mon, 10 Mar 2025 12:34:30 -0300
Ariel D'Alessandro <ariel.dalessandro@...labora.com> wrote:

> Hi Boris,
> 
> On 2/27/25 11:55 AM, Boris Brezillon wrote:
> > On Wed, 26 Feb 2025 15:30:42 -0300
> > Ariel D'Alessandro <ariel.dalessandro@...labora.com> wrote:
> >   
> >> @@ -642,8 +713,15 @@ struct panfrost_mmu *panfrost_mmu_ctx_create(struct panfrost_device *pfdev)
> >>   		.iommu_dev	= pfdev->dev,
> >>   	};
> >>   
> >> -	mmu->pgtbl_ops = alloc_io_pgtable_ops(ARM_MALI_LPAE, &mmu->pgtbl_cfg,
> >> -					      mmu);
> >> +	if (panfrost_has_hw_feature(pfdev, HW_FEATURE_AARCH64_MMU)) {
> >> +		fmt = ARM_64_LPAE_S1;
> >> +		mmu->enable = mmu_lpae_s1_enable;
> >> +	} else {
> >> +		fmt = ARM_MALI_LPAE;
> >> +		mmu->enable = mmu_mali_lpae_enable;
> >> +	}  
> > 
> > How about we stick to the legacy pgtable format for all currently
> > supported GPUs, and make this an opt-in property attached to the
> > compatible. This way, we can progressively move away from the legacy
> > format once enough testing has been done, while allowing support for
> > GPUs that can't use the old format because the cachability/shareability
> > configuration is too limited.  
> 
> Indeed, that's a better way to go.
> 
> Specifically, what you mean is: keep the same compatible string and add 
> a new property to the `panfrost_compatible` private data for that 
> specific variant?

Exactly.