linux-kernel - Re: [PATCH] gpio: Add missing open drain/source handling to gpiod_set_value

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Message-ID: <CAMuHMdWT9PZHfJtNmAkTSmkodT9AsMKggvFyXi0jmw8YVw6hCQ@mail.gmail.com>
Date:   Wed, 10 Jan 2018 14:29:51 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Wolfram Sang <wsa@...-dreams.de>,
        Jan Kundrát <jan.kundrat@...net.cz>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, linux-gpio@...r.kernel.org,
        Linux I2C <linux-i2c@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpio: Add missing open drain/source handling to gpiod_set_value_cansleep()

Hi Linus,

On Wed, Jan 10, 2018 at 2:17 PM, Linus Walleij <linus.walleij@...aro.org> wrote:
> On Tue, Jan 9, 2018 at 7:08 PM, Geert Uytterhoeven
> <geert+renesas@...der.be> wrote:
>
>> Since commit f11a04464ae57e8d ("i2c: gpio: Enable working over slow
>> can_sleep GPIOs"), probing the i2c RTC connected to an i2c-gpio bus on
>> r8a7740/armadillo fails with:
>>
>>     rtc-s35390a 0-0030: error resetting chip
>>     rtc-s35390a: probe of 0-0030 failed with error -5
>>
>> More debug code reveals:
>>
>>     i2c i2c-0: master_xfer[0] R, addr=0x30, len=1
>>     i2c i2c-0: NAK from device addr 0x30 msg #0
>>     s35390a_get_reg: ret = -6
>>
>> Commit 02e479808b5d62f8 ("gpio: Alter semantics of *raw* operations to
>> actually be raw") moved open drain/source handling from
>> gpiod_set_raw_value_commit() to gpiod_set_value(), but forgot to take
>> into account that gpiod_set_value_cansleep() also needs this handling.
>> The i2c protocol mandates that i2c signals are open drain, hence i2c
>> communication fails.
>>
>> Fix this by adding the missing handling to gpiod_set_value_cansleep(),
>> using a new common helper __gpiod_set_value_nocheck().
>>
>> Fixes: 02e479808b5d62f8 ("gpio: Alter semantics of *raw* operations to actually be raw")
>> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
>> ---
>> The bad gpio commit is in v4.15-rc1 and later.
>> The i2c commit exposing this is not yet upstream, but in i2c/for-next.
>
> Whoops!
>
> It appears Meltdown and Spectre saves my ass because now I have
> time to get this upstream before v4.15...
>
> Applied for fixes with the following tweaks: I removed the __prefix (I don't
> like them) and added kerneldoc.

Looks good to me (also in git). Thanks!

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds