linux-kernel - Re: [PATCH 1/3 v6] serial: mctrl_gpio: Check if GPIO property exisits before requesting it

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Date:   Fri, 14 Jun 2019 11:04:48 +0200
From:   Yegor Yefremov <yegorslists@...glemail.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Stefan Roese <sr@...x.de>, linux-serial@...r.kernel.org,
        kernel list <linux-kernel@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Giulio Benetti <giulio.benetti@...ronovasrl.com>
Subject: Re: [PATCH 1/3 v6] serial: mctrl_gpio: Check if GPIO property exisits
 before requesting it

On Thu, Jun 13, 2019 at 7:08 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Thu, Jun 13, 2019 at 05:45:40PM +0200, Stefan Roese wrote:
> > This patch adds a check for the GPIOs property existence, before the
> > GPIO is requested. This fixes an issue seen when the 8250 mctrl_gpio
> > support is added (2nd patch in this patch series) on x86 platforms using
> > ACPI.
> >
> > Here Mika's comments from 2016-08-09:
> >
> > "
> > I noticed that with v4.8-rc1 serial console of some of our Broxton
> > systems does not work properly anymore. I'm able to see output but input
> > does not work.
> >
> > I bisected it down to commit 4ef03d328769eddbfeca1f1c958fdb181a69c341
> > ("tty/serial/8250: use mctrl_gpio helpers").
> >
> > The reason why it fails is that in ACPI we do not have names for GPIOs
> > (except when _DSD is used) so we use the "idx" to index into _CRS GPIO
> > resources. Now mctrl_gpio_init_noauto() goes through a list of GPIOs
> > calling devm_gpiod_get_index_optional() passing "idx" of 0 for each. The
> > UART device in Broxton has following (simplified) ACPI description:
> >
> >     Device (URT4)
> >     {
> >         ...
> >         Name (_CRS, ResourceTemplate () {
> >             GpioIo (Exclusive, PullDefault, 0x0000, 0x0000, IoRestrictionOutputOnly,
> >                     "\\_SB.GPO0", 0x00, ResourceConsumer)
> >             {
> >                 0x003A
> >             }
> >             GpioIo (Exclusive, PullDefault, 0x0000, 0x0000, IoRestrictionOutputOnly,
> >                     "\\_SB.GPO0", 0x00, ResourceConsumer)
> >             {
> >                 0x003D
> >             }
> >         })
> >
> > In this case it finds the first GPIO (0x003A which happens to be RX pin
> > for that UART), turns it into GPIO which then breaks input for the UART
> > device. This also breaks systems with bluetooth connected to UART (those
> > typically have some GPIOs in their _CRS).
> >
> > Any ideas how to fix this?
> >
> > We cannot just drop the _CRS index lookup fallback because that would
> > break many existing machines out there so maybe we can limit this to
> > only DT enabled machines. Or alternatively probe if the property first
> > exists before trying to acquire the GPIOs (using
> > device_property_present()).
> > "
> >
> > This patch implements the fix suggested by Mika in his statement above.
> >
>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

I cannot compile the driver without adding #include <linux/property.h>
to drivers/tty/serial/serial_mctrl_gpio.c.

My platform is AM335X (OMAP3). I've tried the patches both against the
main repo and also tty-next.

Other than that everything is working.

Yegor

> > Signed-off-by: Stefan Roese <sr@...x.de>
> > Reviewed-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> > Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>
> > Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > Cc: Yegor Yefremov <yegorslists@...glemail.com>
> > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Cc: Giulio Benetti <giulio.benetti@...ronovasrl.com>
> > ---
> > v6:
> > - No change
> >
> > v5:
> > - Simplified the code a bit (Andy)
> > - Added gpio_str == NULL handling (Andy)
> >
> > v4:
> > - Add missing free() calls (Johan)
> > - Added Mika's reviewed by tag
> > - Added Johan to Cc
> >
> > v3:
> > - No change
> >
> > v2:
> > - Include the problem description and analysis from Mika into the commit
> >   text, as suggested by Greg.
> >
> >  drivers/tty/serial/serial_mctrl_gpio.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> >
> > diff --git a/drivers/tty/serial/serial_mctrl_gpio.c b/drivers/tty/serial/serial_mctrl_gpio.c
> > index 39ed56214cd3..65348887a749 100644
> > --- a/drivers/tty/serial/serial_mctrl_gpio.c
> > +++ b/drivers/tty/serial/serial_mctrl_gpio.c
> > @@ -116,6 +116,19 @@ struct mctrl_gpios *mctrl_gpio_init_noauto(struct device *dev, unsigned int idx)
> >
> >       for (i = 0; i < UART_GPIO_MAX; i++) {
> >               enum gpiod_flags flags;
> > +             char *gpio_str;
> > +             bool present;
> > +
> > +             /* Check if GPIO property exists and continue if not */
> > +             gpio_str = kasprintf(GFP_KERNEL, "%s-gpios",
> > +                                  mctrl_gpios_desc[i].name);
> > +             if (!gpio_str)
> > +                     continue;
> > +
> > +             present = device_property_present(dev, gpio_str);
> > +             kfree(gpio_str);
> > +             if (!present)
> > +                     continue;
> >
> >               if (mctrl_gpios_desc[i].dir_out)
> >                       flags = GPIOD_OUT_LOW;
> > --
> > 2.22.0
> >
>
> --
> With Best Regards,
> Andy Shevchenko
>
>