Re: [PATCH 1/2 v9] serial: mctrl_gpio: Check if GPIO property exisits before requesting it

[Stefan Roese]

On 24.06.19 10:42, Geert Uytterhoeven wrote:
> CC gpio
>
> This is now commit d99482673f950817 ("serial: mctrl_gpio: Check if GPIO
> property exisits before requesting it") in tty-next.
>
> On Thu, Jun 20, 2019 at 8:24 AM Stefan Roese <sr@xxxxxxx> 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.
> >
> > Signed-off-by: Stefan Roese <sr@xxxxxxx>
> > Reviewed-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> > Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> > Tested-by: Yegor Yefremov <yegorslists@xxxxxxxxxxxxxx>
> > Cc: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> > Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> > Cc: Yegor Yefremov <yegorslists@xxxxxxxxxxxxxx>
> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Cc: Giulio Benetti <giulio.benetti@xxxxxxxxxxxxxxxx>
> > ---
> > v9:
> > - Rebased on top of "tty-next", patch 2/3 dropped as its already applied
> >
> > v8:
> > - Rebased on top of "tty-next"
> >
> > v7:
> > - Include <linux/property.h> to fix compile breakage on OMAP
> >
> > 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 | 14 ++++++++++++++
> >   1 file changed, 14 insertions(+)
> >
> > diff --git a/drivers/tty/serial/serial_mctrl_gpio.c b/drivers/tty/serial/serial_mctrl_gpio.c
> > index 39ed56214cd3..2b400189be91 100644
> > --- a/drivers/tty/serial/serial_mctrl_gpio.c
> > +++ b/drivers/tty/serial/serial_mctrl_gpio.c
> > @@ -12,6 +12,7 @@
> >   #include <linux/termios.h>
> >   #include <linux/serial_core.h>
> >   #include <linux/module.h>
> > +#include <linux/property.h>
> >
> >   #include "serial_mctrl_gpio.h"
> >
> > @@ -116,6 +117,19 @@ 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);
>
> This will silently break DTBs using "(cts|dsr|dcd|rng|rts|dtr)-gpio" instead
> of "(cts|dsr|dcd|rng|rts|dtr)-gpios".

Should both options be supported ("cts-gpio" vs "cts-gpios")?
Documentation/devicetree/bindings/serial/serial.txt only mentions
the "-gpios" variant.

Thanks,
Stefan