linux-kernel - Re: [PATCH v3 2/2] mtd: rawnand: ingenic: Limit MTD_NAND

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Message-ID: <20200727170302.GA3507@kozik-lap>
Date:   Mon, 27 Jul 2020 19:03:02 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Paul Cercueil <paul@...pouillou.net>,
        Harvey Hunt <harveyhuntnexus@...il.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-mtd <linux-mtd@...ts.infradead.org>
Subject: Re: [PATCH v3 2/2] mtd: rawnand: ingenic: Limit MTD_NAND_JZ4780 to
 architecture only

On Mon, Jul 27, 2020 at 09:55:54AM +0200, Arnd Bergmann wrote:
> On Sun, Jul 26, 2020 at 6:20 PM Paul Cercueil <paul@...pouillou.net> wrote:
> > Le dim. 26 juil. 2020 à 18:15, Krzysztof Kozlowski <krzk@...nel.org> a écrit :
> > > On Sun, Jul 26, 2020 at 06:12:27PM +0200, Paul Cercueil wrote:
> > >>  Le dim. 26 juil. 2020 à 18:06, Krzysztof Kozlowski <krzk@...nel.org> a écrit
>  >
> > > OK, that's true. Anyway, I don't have strong opinion on any of this. I
> > > just followed Arnd's hint.
> > >
> > > For the memory driver (and MTD NAND as well) which one you prefer:
> > > 1. https://lore.kernel.org/lkml/20200724074038.5597-6-krzk@kernel.org/
> > > 2. depends on MACH_INGENIC || MIPS_GENERIC || COMPILE_TEST
> > >
> > > ?
> >
> > I'd say a slightly modified #1. The driver shouldn't be "default y" in
> > the first place, so the patch could be to disable it by default.
> 
> If it defaults to 'n' even for MACH_INGENIC, you may have to enable
> it in the four defconfig files for these machines to avoid surprises.

Exactly. Nothing else selects JZ4780_NEMC, so either we keep default y
("if MACH_INGENIC || MIPS_GENERIC"), or you select it directly from
MACH_INGENIC/MIPS_GENERIC.

A related question is how essential are these drivers? At least for ARM
platforms, all essential SoC blocks/IPs are selected by default, if
support for chosen SoC is enabled. Only non-essential stuff is left,
e.g. DRM, cpufreq, devfreq, ADC, crypto, video, USB, eMMC (although one
could argue that it is essential), IOMMU.

> > And when the Ingenic code is merged into the MIPS generic framework, I'll
> > send a set of patches to change all driver dependencies on MIPS to
> > MIPS_GENERIC.
> 
> The way we do it on Arm, the machine Kconfig identifiers stay around
> even for multiplatform targets (which now make up basically actively
> maintained machines).
> 
> I don't think it makes any sense for a driver to depend on MIPS_GENERIC:
> either it is a generic driver that should always be visible or it is specific
> to a set of SoCs and should depend on some corresponding vendor
> specific identifiers.

If support for Ingenic is provided also by MIPS_GENERIC (without
selecting MACH_INGENIC), then it makes sense. This would be just a
different way than ARM of building multi-platform kernel.

Best regards,
Krzysztof