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

[Stefan Roese]

On 14.06.19 11:04, Yegor Yefremov wrote:
> On Thu, Jun 13, 2019 at 7:08 PM Andy Shevchenko
> <andriy.shevchenko@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
>
> 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.

Thanks for reporting. I'll wait a bit for other review comments and
tests (thanks Andy) and will then send v7 with this header included
(and compile tested on OMAP3) later next week.

BTW: Could you please add a Tested-by-tag with the next version?

Thanks,
Stefan