linux-kernel - Re: [PATCH 2/4] dt-bindings: media: Add bindings for raspberrypi,rp1-cfe

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Message-ID: <CAEmqJPohq1Y11uwBWdGGX3B1vPLEK9_A7OQC=-k+bHcdk3n=mQ@mail.gmail.com>
Date: Tue, 19 Mar 2024 15:32:43 +0000
From: Naushir Patuck <naush@...pberrypi.com>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>, linux-media@...r.kernel.org, 
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-rpi-kernel@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org, 
	Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
	Sakari Ailus <sakari.ailus@...ux.intel.com>, Jacopo Mondi <jacopo.mondi@...asonboard.com>, 
	Kieran Bingham <kieran.bingham@...asonboard.com>, 
	Mauro Carvalho Chehab <mchehab@...nel.org>, 
	Raspberry Pi Kernel Maintenance <kernel-list@...pberrypi.com>, Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Florian Fainelli <florian.fainelli@...adcom.com>, 
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>
Subject: Re: [PATCH 2/4] dt-bindings: media: Add bindings for raspberrypi,rp1-cfe

On Tue, 19 Mar 2024 at 14:03, Tomi Valkeinen
<tomi.valkeinen@...asonboard.com> wrote:
>
> On 19/03/2024 15:05, Naushir Patuck wrote:
> > On Tue, 19 Mar 2024 at 13:02, Krzysztof Kozlowski
> > <krzysztof.kozlowski@...aro.org> wrote:
> >>
> >> On 19/03/2024 13:57, Naushir Patuck wrote:
> >>>>>>
> >>>>>> See writing bindings. Compatibles should be SoC specific. In some cases
> >>>>>> generic fallbacks make sense, in some note. But don't just choose
> >>>>>> "generic fallback" because you want. Provide rationale.
> >>>>>
> >>>>> If the compatible is SoC specific, I suppose "raspberrypi,rp1-cfe"
> >>>>> would be the correct string.
> >>>>
> >>>> Sure, but then please think what if rp1 is on Rpi6, called exactly the
> >>>> same (rp1), with some minor differences? Could it be?
> >>>
> >>> Yes, this is definitely possible.  In such cases, I would expect the
> >>> hardware to have a version register that would be queried by the
> >>> driver to adjust for minor differences, and the compatible string
> >>> remains the same.  Does that seem reasonable?
> >>
> >> The "would expect" is concerning. The register(s) must be there already,
> >> with proper value.
> >>
> >
> > A version register already exists in the current hardware, so we will
> > update it to identify future hardware revisions.
>
> But that's a version register for the FE block, not for the whole
> module, right? Are you suggesting that you'll make sure the FE version
> will be changed every time anything in the bigger CFE block is changed,
> and thus the FE version would also reflect the whole CFE version?

Yes, we will update the FE versioning when either CSI2 / FE blocks are updated.

>
> Can there be versions without the FE block, with just the CSI-2 parts?

There is no version register just in the CSI2 block in isolation, so
this is not possible.

>
> Also, I'm still wondering about the RP1 part there in the compatible
> string. Is it necessary? The CFE is located in the RP1 co-processor, but
> is that relevant?
>
> Is there a versioning for the whole RP1 chip? Maybe it's going to the
> wrong direction if we use the board/SoC for this compatible name, as
> it's actually the RP1 where the CFE is located in, not the SoC.
>

I don't really know the conversion required to answer this one.
Logically CFE is on RP1, so it makes sense to me to have "rp1" in the
string, but I will follow the judgment of the maintainers.

Regards,
Naush