linux-kernel - Re: [PATCH 1/1] arm64: Kconfig: Enable PINCTRL on i.MX platforms

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Message-ID: <87a57nxogy.fsf@geanix.com>
Date: Thu, 08 May 2025 14:43:09 +0200
From: Esben Haabendal <esben@...nix.com>
To: "Alexander Stein" <alexander.stein@...tq-group.com>
Cc: "Catalin Marinas" <catalin.marinas@....com>,  "Will Deacon"
 <will@...nel.org>,  "Stefan Wahren" <wahrenst@....net>,
  <linux-arm-kernel@...ts.infradead.org>,  <linux-kernel@...r.kernel.org>,
  "Shawn Guo" <shawnguo@...nel.org>
Subject: Re: [PATCH 1/1] arm64: Kconfig: Enable PINCTRL on i.MX platforms

"Alexander Stein" <alexander.stein@...tq-group.com> writes:

> Hi Esben,
>
> Am Donnerstag, 8. Mai 2025, 10:18:35 CEST schrieb Esben Haabendal:
>> "Alexander Stein" <alexander.stein@...tq-group.com> writes:
>>
>> > Hi Esben,
>> >
>> > Am Donnerstag, 8. Mai 2025, 08:44:22 CEST schrieb Esben Haabendal:
>> >> "Alexander Stein" <alexander.stein@...tq-group.com> writes:
>> >>
>> >> > Hi Stefan,
>> >> >
>> >> > Am Mittwoch, 7. Mai 2025, 16:30:33 CEST schrieb Stefan Wahren:
>> >> >> Hi Alexander,
>> >> >>
>> >> >> [add Shawn and Esben]
>> >> >>
>> >> >> Am 07.05.25 um 14:44 schrieb Alexander Stein:
>> >> >> > Select PINCTRL for NXP i.MX SoCs.
>> >> >> could you please explain the motivation behind your change?
>> >> >>
>> >> >> Is it related to this commit 17d21001891402 ("ARM: imx: Allow user to
>> >> >> disable pinctrl")?
>> >> >
>> >> > Ah, thanks for the pointer. It might be the case.
>> >>
>> >> The goal of the patch mentioned above was to be able to build a kernel
>> >> for LS1021A without pinctrl framework enabled, as LS1021A does not have
>> >> a pinctrl driver.
>> >>
>> >> With your patch, that would not be possible anymore.
>> >
>> > Why? LS1021A is arm, not arm64 which this patch is touching only.
>>
>> Good point :)  Sorry about that.
>>
>> > BTW: Commit b77bd3ba762f3 ("ARM: imx: Re-introduce the PINCTRL selection")
>> > is actually doing the same for arm as there is some fallout from
>> > 17d21001891402.
>> >
>> >> > I noticed that, when using arch/arm64/defconfig and disabling all
>> >> > platforms despite ARCH_MXC before running make olddefconfig,
>> >> > CONFIG_PINCTRL gets disabled as well. No platform is enabling it. I
>> >> > noticed this when building in yocto and non-IMX platforms are disabled
>> >> > for build time reasons.
>> >>
>> >> But is that something that needs to be fixed?
>> >>
>> >> It sounds like quite a special use-case, and why not simply enable
>> >> CONFIG_PINCTRL in that case then?
>> >
>> > PINCTRL is crucial for any SoC to even boot, so this is an option which has
>> > to be set if that platform is enabled.
>>
>> Yes, but PINCTRL (framework) does not by itself do anything meaningful.
>> You need the correct pinctrl driver.
>>
>> Making the various SOC's select the corresponding pinctrl drivers makes
>> sense if it is required for booting under all circumstances. And this
>> should then indirectly enable/select PINCTRL and anything else needed
>> for that driver.
>
> If you prefer I don't mind enabling PINCTRL and the SoC-specific driver
> (e.g. PINCTRL_IMX8MP) depending on each SoC-support, e.g. SOC_IMX35 or
> SOC_IMX8M.

For SOC_IMX35, it should be selected by default.

    config PINCTRL_IMX35
            bool "IMX35 pinctrl driver"
            depends on OF
            depends on SOC_IMX35 || COMPILE_TEST
            default SOC_IMX35

For the IMX8M* SoC's, that is not done, as there is only a common
SOC_IMX8M config entry, which corresponds to multiple pinctrl drivers,
which we probably don't want to select all of by default.

>> Having ARCH_MXC select PINCTRL as such is mostly pointless IMHO.
>> Enabling a driver framework without enabling any drivers for it, when
>> building a kernel where no SOC's requiring any pinctrl drivers is kind
>> of weird. If you want to do that, why not simply enable both ARCH_MXC
>> and PINCTRL in your yocto recipe?
>
> PINCTRL is currently only enabled because other SoCs happen to enable it,
> just this feels just plain wrong. If these platforms are disabled or
> removed for whatever reason, the other platforms should still work.

As it is now, to build for let's say i.MX 8M Plus, you have to enable
    SOC_IMX8M
    PINCTRL_IMX8MP
to get a kernel that is likely to boot.

If you enable
    SOC_IMX8M
    PINCTRL
but not
    PINCTRL_IMX8MP
you won't have pinctrl support, and the kernel will probably not work as
expected.

What am I missing?

/Esben