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Date:   Fri, 14 Jun 2019 11:29:29 +0200
From:   Stefan Roese <>
To:     Yegor Yefremov <>,
        Andy Shevchenko <>
        kernel list <>,
        Mika Westerberg <>,
        Greg Kroah-Hartman <>,
        Giulio Benetti <>
Subject: Re: [PATCH 1/3 v6] serial: mctrl_gpio: Check if GPIO property exisits
 before requesting it

On 14.06.19 11:04, Yegor Yefremov wrote:
> On Thu, Jun 13, 2019 at 7:08 PM Andy Shevchenko
> <> 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 <>
> 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?


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