linux-kernel - Re: tty/serial/8250: use mctrl_gpio helpers

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Date:	Tue, 09 Aug 2016 19:07:21 +0300
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Yegor Yefremov <yegorslists@...glemail.com>,
	Peter Hurley <peter@...leysoftware.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: tty/serial/8250: use mctrl_gpio helpers - Causes problems on
 ACPI systems

+Peter

On Tue, 2016-08-09 at 16:02 +0300, Mika Westerberg wrote:
> Hi,
> 
> 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").

Mika, thanks for the detailed analysis. 
Yegor, consider this mail as a follow up to [1].

[1] http://www.spinics.net/lists/linux-serial/msg23071.html

> 
> 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()).

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy