Messages in this thread | | | Subject | Re: [PATCH 1/2 v2] serial: mctrl_gpio: Check if GPIO property exisits before requesting it | From | Giulio Benetti <> | Date | Fri, 24 May 2019 14:09:16 +0200 |
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Hello Stefan,
Il 24/05/2019 13:29, Stefan Roese ha scritto: > On 24.05.19 13:11, Andy Shevchenko wrote: >> On Fri, May 24, 2019 at 1:21 PM Mika Westerberg >> <mika.westerberg@linux.intel.com> wrote: >>> >>> On Fri, May 24, 2019 at 11:48:24AM +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. >>>> >> >> We have a board where ASL provides _DSD for CTS and RxD pins. >> I'm afraid this won't work on it. > > With "won't work" you mean, that the GPIO can't be used for modem > control in this case in the current implementation (with this > patchset)? Or do you mean, that the breakage (input does not work > on Broxton systems) will not be solved by this patch? > > If its the former, then I think that solving this issue is something > for a new patch, to support modem-control on such platforms as well > (if needed). > > Please note that this patch is not trying to get modem-control working > on such ACPI based systems. Its targeted for device-tree enabled > platforms, using the 8250 serial driver, here specifically a MIPS > MT7688 based board. And just wants to fix the latter issue mentioned > above so that the 8250 modem-control support can be accepted in > mainline.
Take a look here: https://lkml.org/lkml/2018/6/5/253
It's about waking up 8250 UART. As I remember that is the problem. I wanted to try to fix it but had no time.
What it broken as I remember is the capability to wake up linux on uart RX. Hope I've understood right at that time.
Best regards -- Giulio Benetti CTO
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>> Basically we need to understand the use of the GPIOs in UART. In our >> case it's an out-of-band wake up source for UART. >> Simply requiring GPIOs to be present is not enough. >> >> Perhaps property like 'modem-control-gpio-in-use' (this seems a bad >> name, given for sake of example). > > Thanks, > Stefan >
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