Messages in this thread | | | Subject | Re: [PATCH 1/2 v9] serial: mctrl_gpio: Check if GPIO property exisits before requesting it | From | Stefan Roese <> | Date | Tue, 25 Jun 2019 07:27:33 +0200 |
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Hi Geert,
On 24.06.19 17:35, Geert Uytterhoeven wrote: > On Mon, Jun 24, 2019 at 5:29 PM Stefan Roese <sr@denx.de> wrote: >> On 24.06.19 10:42, Geert Uytterhoeven wrote: >>> On Thu, Jun 20, 2019 at 8:24 AM Stefan Roese <sr@denx.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@denx.de> > >>>> --- a/drivers/tty/serial/serial_mctrl_gpio.c >>>> +++ b/drivers/tty/serial/serial_mctrl_gpio.c > >>>> @@ -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. > > Well, the "-gpio" variant is deprecated, but still supported by > devm_gpiod_get_index_optional(), and there are active users in upstream > DTS files. > > My main objection is (trying to) replicate the matching logic inside > gpiolib.c, causing subtle semantic differences. And keeping it consistent, > of course. > > It would be nice if this could be fixed inside acpi_find_gpio(), so > users don't need to be updated. There may be other subsystems where > the difference between DT and ACPI may cause issues, unbeknownst.
Sure, I can fix this. I would prefer to do this in a follow-up patch though, if nobody objects.
Thanks, Stefan
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