linux-kernel - Re: [PATCH 1/4] media: dt-bindings: cedrus: Allow power domain references

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Date:   Thu, 5 Jan 2023 08:48:52 -0600
From:   Samuel Holland <samuel@...lland.org>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Cc:     Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Conor Dooley <conor@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Maxime Ripard <mripard@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-staging@...ts.linux.dev,
        linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH 1/4] media: dt-bindings: cedrus: Allow power domain
 references

Hi Paul,

On 1/5/23 04:43, Paul Kocialkowski wrote:
> On Sat 31 Dec 22, 10:46, Samuel Holland wrote:
>> The Allwinner D1 SoC contains a separate power domain for its video
>> engine, controlled via the "PPU" power controller. Allow the
>> power-domains property so this can be represented in the devicetree.
> 
> I've been looking around for information regarding the PPU and couldn't find
> anything about it. Do you have some reference where it is mentionned?

There are some oblique references as far back as H6 in some user manuals
(in the bus block diagram and interrupt list) and in the vendor clock
drivers.

I gathered some information here:
https://linux-sunxi.org/PPU

It is used by OpenSBI for CPU idle:
https://github.com/riscv-software-src/opensbi/commit/9dc5ec5c.patch

and I have a series adding PPU support to Linux for the Video Engine:
https://lore.kernel.org/linux-sunxi/20221231160402.16157-1-samuel@sholland.org/

> I do see a power domain driver (apparently for the GPU) on recent allwinner
> kernel releases but that seems to be for arm64 chips only.

Yes, there is an older GPU-specific power domain hardware, and the
generic one found on D1/R528/T113 and newer. However, I found while
writing the Linux driver that the two are more similar than the vendor
drivers would imply. Most of the registers from the old hardware remain
in the new hardware; they just are not used by the new vendor driver. So
you can reference my Linux series for a full register list.

Regards,
Samuel

>> Signed-off-by: Samuel Holland <samuel@...lland.org>
>> ---
>>
>>  .../bindings/media/allwinner,sun4i-a10-video-engine.yaml       | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/media/allwinner,sun4i-a10-video-engine.yaml b/Documentation/devicetree/bindings/media/allwinner,sun4i-a10-video-engine.yaml
>> index 541325f900a1..d5be7f604e8c 100644
>> --- a/Documentation/devicetree/bindings/media/allwinner,sun4i-a10-video-engine.yaml
>> +++ b/Documentation/devicetree/bindings/media/allwinner,sun4i-a10-video-engine.yaml
>> @@ -63,6 +63,9 @@ properties:
>>        CMA pool to use for buffers allocation instead of the default
>>        CMA pool.
>>  
>> +  power-domains:
>> +    maxItems: 1
>> +
>>  required:
>>    - compatible
>>    - reg
>> -- 
>> 2.37.4
>>
>