Re: [GIT PULL] ARM: mvebu: dt64 for v7.2 (#1)

Hello Arnd,

> On Tue, Jun 9, 2026, at 21:29, Arnd Bergmann wrote:
>> On Tue, Jun 9, 2026, at 19:35, Aleksander Jan Bajkowski wrote:
>>> On 09/06/2026 18:11, Arnd Bergmann wrote:
>>>> I'm a bit surprised by this oneline change. Since you successfully tested
>>>> this, I assume the change is correct, but I have two questions that
>>>> I would like to have an answer for before I pull it.
>>> By the way, the upstream safexcel driver works correctly only on 
>>> coherent
>>> platforms. On non-coherent platforms (MediaTek), the SHA-384 and SHA-512
>>> selftests fail. Since the selftests pass on Armada's SoC, I assume I'm 
>>> right.
>>
>> It's not necessarily proof that this is correct, but it is quite likely.
>>
>> After checking the datasheet some more and finding that this should
>> indeed be coherent everywhere, I remembered that even the old
>> 32-bit Armada 370 had a coherency manager. At the time, we used a hack
>> in  arch/arm/mach-mvebu/coherency.c to mark all device nodes as coherent,
>> since the original DTB did not contain the correct annotations.
>>
>> I suspect that the Armada 37xx started out with a copy of the
>> old DT files and also never had the annotation, but then never
>> had the same hack because arch/arm64 does not have platform
>> specific code.
>
> After investigating a little more, I think the correct fix here
> will be to mark all DMA masters in this SoC as dma-coherent.
> I thought there was a way to do this for an entire system,
> but I could not find that, so this likely has to be done
> for each DMA master separately.

Thanks for doing this research. I also checked the data in the datasheet
before applying the patch, and it appears the platform is coherent. I
was surprised that when we initially submitted the support request,
Marvel didn't mention this; usually, SoC vendors like to have good
performance numbers. However, they also didn't say anything about a
coherence issue. The fact that the test succeeded is a good indicator
that the SoC is indeed coherent.
>
> Not sure who still has the hardware and has time to
> test this properly. Given that the incorrect DT has
> existed for over 10 years now, I assume this is not
> urgent and I will skip the pull request for 7.2.

I believe I still have a board based on an Armada 3700, and I should be
able to find time to do some tests.

Gregory

>
>      Arnd

-- 
Grégory CLEMENT, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com