From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Shevchenko Subject: Re: [PATCH 1/3 v6] serial: mctrl_gpio: Check if GPIO property exisits before requesting it Date: Thu, 13 Jun 2019 20:08:02 +0300 Message-ID: <20190613170802.GE9224@smile.fi.intel.com> References: <20190613154542.32438-1-sr@denx.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190613154542.32438-1-sr@denx.de> Sender: linux-kernel-owner@vger.kernel.org To: Stefan Roese Cc: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Mika Westerberg , Yegor Yefremov , Greg Kroah-Hartman , Giulio Benetti List-Id: linux-serial@vger.kernel.org On Thu, Jun 13, 2019 at 05:45:40PM +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. > Reviewed-by: Andy Shevchenko > Signed-off-by: Stefan Roese > Reviewed-by: Mika Westerberg > Cc: Mika Westerberg > Cc: Andy Shevchenko > Cc: Yegor Yefremov > Cc: Greg Kroah-Hartman > Cc: Giulio Benetti > --- > 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 | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/drivers/tty/serial/serial_mctrl_gpio.c b/drivers/tty/serial/serial_mctrl_gpio.c > index 39ed56214cd3..65348887a749 100644 > --- a/drivers/tty/serial/serial_mctrl_gpio.c > +++ b/drivers/tty/serial/serial_mctrl_gpio.c > @@ -116,6 +116,19 @@ 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; > + > + present = device_property_present(dev, gpio_str); > + kfree(gpio_str); > + if (!present) > + continue; > > if (mctrl_gpios_desc[i].dir_out) > flags = GPIOD_OUT_LOW; > -- > 2.22.0 > -- With Best Regards, Andy Shevchenko