linux-kernel - Re: Bug introduced in the of_get_named_gpiod

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Message-ID: <CACRpkdYQBxvHh-AfODddzc5G+BMBhUBSRXUdLVO8_99yniUYPQ@mail.gmail.com>
Date:   Thu, 11 Oct 2018 10:27:45 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     wzab@....pw.edu.pl, Randy Dunlap <rdunlap@...radead.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Michal Simek <michal.simek@...inx.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Bug introduced in the of_get_named_gpiod_flags function.

Hi Wojciech,

(Thanks also Randy for forwarding this!)

On Wed, Oct 10, 2018 at 6:32 PM wzab <wzab@....pw.edu.pl> wrote:

> The function of_get_named_gpiod_flags in older versions of the kernel
> (up to 4.7.10 - https://elixir.bootlin.com/linux/v4.7.10/source/drivers/gpio/gpiolib-of.c#L75 )
> contained an important workaround:
>
> /* .of_xlate might decide to not fill in the flags, so clear it. */if (flags)
>    *flags = 0; Unfortunately, newer kernels do not contain it. Therefore if the
> "xlat" function in the gpiochip driver does not set flags, (like e.g.
> the Xilinx AXI GPIO driver: https://github.com/Xilinx/linux-xlnx/blob/c2ba891326bb472da59b6a2da29aca218d337687/drivers/gpio/gpio-xilinx.c#L262 )
> the random, unitialized value from the stack in of_find_gpio
> ( https://elixir.bootlin.com/linux/v4.18.13/source/drivers/gpio/gpiolib-of.c#L228 )
> is used, which results in random settings of e.g., OPEN DRAIN or OPEN SOURCE mode.
>
> I have also reported the problem in the Xilinx forum:
> https://forums.xilinx.com/t5/Embedded-Linux/Bug-in-of-get-named-gpiod-flags-function-in-the-kernel-random/td-p/897695

It seems the commit removing this is:

commit 762c2e46c0591d207289105c8718e4adf29b2b34
"gpio: of: remove of_gpiochip_and_xlate() and struct gg_data"

But I honestly don't see a problem with it.

You are referencing an out-of-tree driver. Use the in-tree gpio-xilinx.c
that does not do any custom xlate and you will be fine.

I looked over the driver doing custom flag translation in the kernel tree,
and they all set flags, so this is not a problem in the upstream kernel.

Yours,
Linus Walleij