linux-kernel - Re: [PATCH] arm64: dts: allwinner: Add cache information to the SoC dtsi for H6

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Date: Tue, 30 Apr 2024 13:10:41 +0200
From: Dragan Simic <dsimic@...jaro.org>
To: Andre Przywara <andre.przywara@....com>
Cc: linux-sunxi@...ts.linux.dev, wens@...e.org, jernej.skrabec@...il.com,
 samuel@...lland.org, linux-arm-kernel@...ts.infradead.org,
 devicetree@...r.kernel.org, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: allwinner: Add cache information to the SoC
 dtsi for H6

Hello Andre,

On 2024-04-30 12:46, Andre Przywara wrote:
> On Tue, 30 Apr 2024 02:01:42 +0200
> Dragan Simic <dsimic@...jaro.org> wrote:
>> On 2024-04-30 01:10, Andre Przywara wrote:
>> > On Sun, 28 Apr 2024 13:40:36 +0200
>> > Dragan Simic <dsimic@...jaro.org> wrote:
>> >
>> >> Add missing cache information to the Allwinner H6 SoC dtsi, to allow
>> >> the userspace, which includes lscpu(1) that uses the virtual files
>> >> provided
>> >> by the kernel under the /sys/devices/system/cpu directory, to display
>> >> the
>> >> proper H6 cache information.
>> >>
>> >> Adding the cache information to the H6 SoC dtsi also makes the
>> >> following
>> >> warning message in the kernel log go away:
>> >>
>> >>   cacheinfo: Unable to detect cache hierarchy for CPU 0
>> >>
>> >> The cache parameters for the H6 dtsi were obtained and partially
>> >> derived
>> >> by hand from the cache size and layout specifications found in the
>> >> following
>> >> datasheets and technical reference manuals:
>> >>
>> >>   - Allwinner H6 V200 datasheet, version 1.1
>> >>   - ARM Cortex-A53 revision r0p3 TRM, version E
>> >>
>> >> For future reference, here's a brief summary of the documentation:
>> >>
>> >>   - All caches employ the 64-byte cache line length
>> >>   - Each Cortex-A53 core has 32 KB of L1 2-way, set-associative
>> >> instruction
>> >>     cache and 32 KB of L1 4-way, set-associative data cache
>> >>   - The entire SoC has 512 KB of unified L2 16-way, set-associative
>> >> cache
>> >>
>> >> Signed-off-by: Dragan Simic <dsimic@...jaro.org>
>> >
>> > I can confirm that the data below matches the manuals, but also the
>> > decoding of the architectural cache type registers (CCSIDR_EL1):
>> >   L1D: 32 KB: 128 sets, 4 way associative, 64 bytes/line
>> >   L1I: 32 KB: 256 sets, 2 way associative, 64 bytes/line
>> >   L2: 512 KB: 512 sets, 16 way associative, 64 bytes/line
>> 
>> Thank you very much for reviewing my patch in such a detailed way!
>> It's good to know that the values in the Allwinner datasheets match
>> with the observed reality, so to speak. :)
> 
> YW, and yes, I like to double check things when it comes to Allwinner
> documentation ;-) And it was comparably easy for this problem.

Double checking is always good, IMHO. :)

> Out of curiosity: what triggered that patch? Trying to get rid of false
> warning/error messages?

Yes, one of the motivators was to get rid of the false kernel warning,
and the other was to have the cache information nicely available through
lscpu(1).  I already did the same for a few Rockchip SoCs, [1][2][3] so
a couple of Allwinner SoCs were the next on my mental TODO list. :)

> And do you plan to address the H616 as well? It's a bit more tricky 
> there,
> since there are two die revisions out: one with 256(?)KB of L2, one 
> with
> 1MB(!). We know how to tell them apart, so I could provide some TF-A 
> code
> to patch that up in the DT. The kernel DT copy could go with 256KB 
> then.

I have no boards based on the Allwinner H616, so it wasn't on my radar.
Though, I'd be happy to prepare and submit a similar kernel patch for
the H616, if you'd then take it further and submit a TF-A patch that
fixes the DT according to the detected die revision?  Did I understand
the plan right?

[1] 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=67a6a98575974416834c2294853b3814376a7ce7
[2] 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=8612169a05c5e979af033868b7a9b177e0f9fcdf
[3] 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=b72633ba5cfa932405832de25d0f0a11716903b4