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