Hello,
On Thu, Jun 20, 2019 at 08:24:19AM +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@xxxxxxx>
> Reviewed-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Tested-by: Yegor Yefremov <yegorslists@xxxxxxxxxxxxxx>
> Cc: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Cc: Yegor Yefremov <yegorslists@xxxxxxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Giulio Benetti <giulio.benetti@xxxxxxxxxxxxxxxx>
> ---
> 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);
> + if (!gpio_str)
> + continue;
Is it a good idea to handle a memory allocation problem with a continue?
> + present = device_property_present(dev, gpio_str);
> + kfree(gpio_str);
> + if (!present)
> + continue;
>
Assuming this fixes the situation on x86 this means that there
device_property_present(...) returns false and
devm_gpiod_get_index_optional returns an error code.
I wonder what the problem is here. Is CONFIG_GPIOLIB on in the failing
situation?
I assume this will end in the usual discussion if gpiod_get_*_optional
should return an error code if GPIOLIB is off.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
