Date:   Mon, 24 Jun 2019 17:29:24 +0200
From:   Stefan Roese <sr@...x.de>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Yegor Yefremov <yegorslists@...glemail.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Giulio Benetti <giulio.benetti@...ronovasrl.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH 1/2 v9] serial: mctrl_gpio: Check if GPIO property exisits
 before requesting it

On 24.06.19 10:42, Geert Uytterhoeven wrote:
> CC gpio
> 
> This is now commit d99482673f950817 ("serial: mctrl_gpio: Check if GPIO
> property exisits before requesting it") in tty-next.
> 
> On Thu, Jun 20, 2019 at 8:24 AM Stefan Roese <sr@...x.de> 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>
>> Reviewed-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
>> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
>> Tested-by: Yegor Yefremov <yegorslists@...glemail.com>
>> Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>
>> Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
>> Cc: Yegor Yefremov <yegorslists@...glemail.com>
>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> Cc: Giulio Benetti <giulio.benetti@...ronovasrl.com>
>> ---
>> v9:
>> - Rebased on top of "tty-next", patch 2/3 dropped as its already applied
>>
>> v8:
>> - Rebased on top of "tty-next"
>>
>> v7:
>> - Include <linux/property.h> to fix compile breakage on OMAP
>>
>> v6:
>> - No change
>>
>> v5:
>> - Simplified the code a bit (Andy)
>> - Added gpio_str == NULL handling (Andy)
>>
>> v4:
>> - Add missing free() calls (Johan)
>> - Added Mika's reviewed by tag
>> - Added Johan to Cc
>>
>> v3:
>> - No change
>>
>> v2:
>> - Include the problem description and analysis from Mika into the commit
>>    text, as suggested by Greg.
>>
>>   drivers/tty/serial/serial_mctrl_gpio.c | 14 ++++++++++++++
>>   1 file changed, 14 insertions(+)
>>
>> diff --git a/drivers/tty/serial/serial_mctrl_gpio.c b/drivers/tty/serial/serial_mctrl_gpio.c
>> index 39ed56214cd3..2b400189be91 100644
>> --- a/drivers/tty/serial/serial_mctrl_gpio.c
>> +++ b/drivers/tty/serial/serial_mctrl_gpio.c
>> @@ -12,6 +12,7 @@
>>   #include <linux/termios.h>
>>   #include <linux/serial_core.h>
>>   #include <linux/module.h>
>> +#include <linux/property.h>
>>
>>   #include "serial_mctrl_gpio.h"
>>
>> @@ -116,6 +117,19 @@ struct mctrl_gpios *mctrl_gpio_init_noauto(struct device *dev, unsigned int idx)
>>
>>          for (i = 0; i < UART_GPIO_MAX; i++) {
>>                  enum gpiod_flags flags;
>> +               char *gpio_str;
>> +               bool present;
>> +
>> +               /* Check if GPIO property exists and continue if not */
>> +               gpio_str = kasprintf(GFP_KERNEL, "%s-gpios",
>> +                                    mctrl_gpios_desc[i].name);
> 
> This will silently break DTBs using "(cts|dsr|dcd|rng|rts|dtr)-gpio" instead
> of "(cts|dsr|dcd|rng|rts|dtr)-gpios".

Should both options be supported ("cts-gpio" vs "cts-gpios")?
Documentation/devicetree/bindings/serial/serial.txt only mentions
the "-gpios" variant.

Thanks,
Stefan

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