linux-kernel - Re: [PATCH 1/2 v3] serial: mctrl_gpio: Check if GPIO property exisits before requesting it

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Message-ID: <20190528100042.GT2781@lahna.fi.intel.com>
Date:   Tue, 28 May 2019 13:00:42 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Stefan Roese <sr@...x.de>
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Yegor Yefremov <yegorslists@...glemail.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Giulio Benetti <giulio.benetti@...ronovasrl.com>
Subject: Re: [PATCH 1/2 v3] serial: mctrl_gpio: Check if GPIO property
 exisits before requesting it

On Mon, May 27, 2019 at 01:18:04PM +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.
> 
> Signed-off-by: Stefan Roese <sr@...x.de>
> Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>

Reviewed-by: Mika Westerberg <mika.westerberg@...ux.intel.com>