RE: [PATCH 3/3] tty: serial: samsung: Remove unused artpec-8 specific code

["Ravi Patel" <ravi.patel@samsung.com>]

> -----Original Message-----
> From: Krzysztof Kozlowski <krzk@kernel.org>
> Sent: 11 September 2025 22:52
> To: Ravi Patel <ravi.patel@samsung.com>; 'Geert Uytterhoeven' <geert@linux-m68k.org>
> Cc: gregkh@linuxfoundation.org; jirislaby@kernel.org; robh@kernel.org; krzk+dt@kernel.org; conor+dt@kernel.org;
> jesper.nilsson@axis.com; lars.persson@axis.com; alim.akhtar@samsung.com; arnd@kernel.org; andriy.shevchenko@linux.intel.com;
> geert+renesas@glider.be; thierry.bultel.yh@bp.renesas.com; dianders@chromium.org; robert.marko@sartura.hr; schnelle@linux.ibm.com;
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> Subject: Re: [PATCH 3/3] tty: serial: samsung: Remove unused artpec-8 specific code
> 
> On 11/09/2025 18:04, Ravi Patel wrote:
> >>>>> -OF_EARLYCON_DECLARE(artpec8, "axis,artpec8-uart",
> >>>>> -                       s5pv210_early_console_setup);
> >>>>>
> >>>>>  static int __init gs101_early_console_setup(struct earlycon_device *device,
> >>>>>                                             const char *opt)
> >>>>
> >>>> Removing these breaks backwards-compatibility with existing DTBs,
> >>>> which lack the new "samsung,exynos8895-uart" fallback compatible value.
> >>>
> >>> This was just applied, so ABI break would be fine. It should be however
> >>> clearly expressed in the commit msg.
> >>>
> >>> I have a feeling that not much testing was happening in Samsung around
> >>> this patchset and only now - after I applied it - some things happen.
> >>> But it is damn too late, my tree is already closed which means this is
> >>> going to be the ABI.
> >>
> >> Ah, no, I mixed up patches with recent DTS for Artpec-8. This serial ABI
> >> was accepted three years ago (!!!), so you are Geert absolutely right -
> >> that's ABI break.
> >
> > Thank you for your review.
> >
> > The DTS patches for ARTPEC-8 is added recently (https://lore.kernel.org/linux-samsung-soc/20250901051926.59970-1-
> ravi.patel@samsung.com/)
> > Before that, there was no user (in DT) of "axis,artpec8-uart" compatible.
> > So I am not convinced of ABI break (considering patch #1 and #2 goes first with review comment fixes)
> 
> 
> ABI is defined by bindings and implemented by kernel. Having DTS user is
> irrelevant to fact whether ABI is or is not broken.
> 
> Having DTS user determines the known impact of known ABI breakage.

OK. So does that mean if someone adds the ABI then it cannot be reverted,
because of it breaks backword compatibility (users are using ABI in their local DTB) ?

Please suggest what should be the proper way.

Thanks,
Ravi

> 
> Best regards,
> Krzysztof