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

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Message-ID: <46456505-0267-4274-a8e4-35c6ece420e5@collabora.com>
Date: Fri, 7 Mar 2025 11:42:56 -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

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@...labora.com> 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@...labora.com>
>> ---
>>   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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