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

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Message-ID: <ec151d39-2cb2-4f67-a23a-dafc421fff75@collabora.com>
Date: Mon, 10 Mar 2025 12:34:30 -0300
From: Ariel D'Alessandro <ariel.dalessandro@...labora.com>
To: Boris Brezillon <boris.brezillon@...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

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? E.g.

In drivers/gpu/drm/panfrost/panfrost_drv.c:
```
struct panfrost_compatible mediatek_mt8188_data
[...]
{ .compatible = "mediatek,mt8188-mali", .data = &mediatek_mt8188_data },
```

Thanks,

-- 
Ariel D'Alessandro
Software Engineer

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