Re: [PATCH 1/2 v2] serial: mctrl_gpio: Check if GPIO property exisits before requesting it

[Stefan Roese]

On 24.05.19 15:46, Andy Shevchenko wrote:
> On Fri, May 24, 2019 at 01:29:34PM +0200, Stefan Roese wrote:
> > On 24.05.19 13:11, Andy Shevchenko wrote:
> > > On Fri, May 24, 2019 at 1:21 PM Mika Westerberg
> > > <mika.westerberg@xxxxxxxxxxxxxxx> wrote:
> > > > On Fri, May 24, 2019 at 11:48:24AM +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.
> > >
> > > We have a board where ASL provides _DSD for CTS and RxD pins.
> > > I'm afraid this won't work on it.
> >
> > With "won't work" you mean, that the GPIO can't be used for modem
> > control in this case in the current implementation (with this
> > patchset)? Or do you mean, that the breakage (input does not work
> > on Broxton systems) will not be solved by this patch?
>
> It will solve RxD case, due to mctrl doesn't count RxD as a "control" line.
>
> Though we have CTS pin defined for the same purpose, which means the hardware
> flow control won't work on a subset of Broxton boards.
>
> > If its the former, then I think that solving this issue is something
> > for a new patch, to support modem-control on such platforms as well
> > (if needed).
>
> > Please note that this patch is not trying to get modem-control working
> > on such ACPI based systems.
>
> I understand that. At the same time it should not break existing systems.
>
> > Its targeted for device-tree enabled
> > platforms, using the 8250 serial driver, here specifically a MIPS
> > MT7688 based board. And just wants to fix the latter issue mentioned
> > above so that the 8250 modem-control support can be accepted in
> > mainline.
>
> As I said already we have to distinguish *the purpose* of these GPIOs.
> (like CTS).
>
> Can we apply this if and only if the device has no ACPI companion device?
>
> In this case DT will work as you expect and ACPI won't be broken.

So your suggestion is to add a has_acpi_companion() check before
mctrl_gpio_init() is called in serial8250_register_8250_port() and
then only use the gpio related mctrl, if the GPIO's are really used?

I can certainly change patch 2/2 to do this. It would be great though,
if you (or someone else) could test this on such a ACPI based platform,
as I don't have access to such a board.

Thanks,
Stefan