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

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Date:	Thu, 18 Aug 2016 11:15:03 +0200
From:	Yegor Yefremov <yegorslists@...glemail.com>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	kernel list <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Subject: Re: tty/serial/8250: use mctrl_gpio helpers - Causes problems on ACPI systems

Hi Uwe,

On Tue, Aug 9, 2016 at 6:07 PM, Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
> +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

Do you have any idea on how to fix this issue?

>> 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