linux-kernel - Re: protected pins and debugfs

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Date:   Thu, 4 Oct 2018 10:34:03 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     psodagud@...eaurora.org
Cc:     Stephen Boyd <sboyd@...eaurora.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-arm-msm@...r.kernel.org
Subject: Re: protected pins and debugfs

On Wed, Oct 3, 2018 at 2:38 PM Sodagudi Prasad <psodagud@...eaurora.org> wrote:

> This is regarding the protected pins configuration reading and printing
> from non-secure operating systems.

I do not think anyone with security in mind should have debugfs
enabled. But maybe that is beside the point.

> GPIO framework is checking whether pin is in use(flag FLAG_REQUESTED) or
> not in gpiolib_dbg_show().
>
> If GPIO chip drivers are overriding the dbg_show callback, drivers are
> not checking whether a pin is really in use or not to print
> configuration details.
>      if (chip->dbg_show)
>                  chip->dbg_show(s, chip);
>          else
>                  gpiolib_dbg_show(s, gdev);

Ah that is right. Because some drivers can inspect all pins whether they
are requested or not.

> Can we use a simple/common solution like below?  It will check whether a
> pin is in use or not before printing configuration data with the help of
> gpiochip_is_requested().

In the msm case I think maybe you want to inspect the valid_mask
instead, so you display debugfs info for all pins you can inspect
in hardware but avoid the "invalid" ones which I half-guess is used
by ACPI in your case.

Yours,
Linus Walleij