Hi Krzysztof Kozlowski,
> -----Original Message-----
> From: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
> Sent: Tuesday, March 12, 2024 10:58 AM
> Subject: Re: [PATCH 4/4] arm64: dts: renesas: r9a07g0{43,44,54}: Update usbhs family compatible
>
> On 11/03/2024 10:03, Geert Uytterhoeven wrote:
> > Hi Krzysztof,
> >
> > On Sat, Mar 9, 2024 at 2:30 PM Krzysztof Kozlowski
> > <krzysztof.kozlowski@xxxxxxxxxx> wrote:
> >> On 09/03/2024 13:32, Biju Das wrote:
> >>>> -----Original Message-----
> >>>> From: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
> >>>>>> This looks like ABI break and commit msg is quite vague about it.
> >>>>>
> >>>>> OK, Will update the commit message as driver is taking care of the
> >>>>> backward compatibility.
> >>>>
> >>>> Ah, I was not precise here, you should consider the impact this is
> >>>> on DTB used on other kernels. You guys should really stop using
> >>>> imprecise/incorrect generic fallbacks and, since it is usually tricky to know which fallback is
> correct or not, you should stop using them at all.
> >>>
> >>> There will be driver change to handle SoC specific compatible.
> >>>
> >>> So ,
> >>>
> >>> old DTB + old kernel will have 16 pipe buffers old DTB + newer
> >>> kernel will have 9 pipe buffers.
> >>> New DTB + new kernel will have 9 pipe buffer.
> >>
> >> You missed new DTB and old kernel. This breaks all users of DTS.
> >> That's the entire point of your broken generic compatibles which you
> >> did not address.
> >
> > Doesn't DT guarantee only forward compatibility?
>
> If by DT you mean DTS, then:
> The DTS is exported from kernel since long time and (might be|is used) in other projects, like recently
> in U-Boot. Therefore dropping compatible from DTS, which is used for binding, might affect these 3rd
> party projects.
>
> While you are right that we do not guarantee such compatibility, we also might want to have it.
If that is the case, the I would like to retain renesas,rzg2l-usbhs for grouping similar RZ/G2L
alike SoCs as in [1]. In the driver, I will use SoC specific compatible to avoid ABI breakage
related to old DTB + new kernel.
[1] https://patchwork.kernel.org/project/linux-renesas-soc/patch/20240308180919.6603-5-biju.das.jz@xxxxxxxxxxxxxx/
Cheers,
Biju
