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    SubjectRe: [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@linux.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@linux.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@denx.de>
    > > Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
    > > Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
    > > Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
    > > Cc: Yegor Yefremov <yegorslists@googlemail.com>
    > > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    > > Cc: Giulio Benetti <giulio.benetti@micronovasrl.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
    >
    >

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