Re: [PATCH] gpiolib-acpi: Set gpiod flags for ACPI GPIO resources based on pullup and polarity

["andriy.shevchenko@xxxxxxxxxxxxxxx" <andriy.shevchenko@xxxxxxxxxxxxxxx>]

On Wed, Dec 04, 2019 at 04:08:34PM +0200, andriy.shevchenko@xxxxxxxxxxxxxxx wrote:
> On Tue, Dec 03, 2019 at 03:24:57PM +0000, Stanimir, Vasile-Laurentiu wrote:
> > On Mon, Dec 02, 2019 at 01:44:04PM +0000, Stanimir, Vasile-Laurentiu wrote:
> > > On Mon, Dec 02, 2019 at 12:36:47PM +0000, Stanimir, Vasile-Laurentiu wrote:

> > The pin itself is a reset pin that must (as defined by rfc2119) be asserted during Linux boot (it controls
> >  the reset logic of a soc external device), the polarity is active low, which is why it's configured with a PullDown. 
> 
> And here is the issue AFAICS. The Active low should be configured with PullUp
> and set to whatever BIOS wants.

I stand corrected:
whatever -> active state

So, basically BIOS settings in ACPI and in hardware should be in align.
Otherwise it's badly created / configured BIOS.

> Correct me if I'm wrong, but code does the following in
> the properly configured DSDT:
> 
> 0/ (not OS) firmware prepares ACPI DSDT with parameters (see 2/) and sets pin
>    to active state - electrical low;
> 1/ we request GPIO via gpiod_get(..., GPIOD_ASIS);
> 2/ ACPI provides: IoOutput + Active Low + PullUp;
> 3/ above is translated to GPIO flags = GPIOD_OUT_HIGH and look up flags =
>    GPIO_PULL_UP | GPIO_ACTIVE_LOW;
> 4/ ...which calls gpiod_direction_output() with value = 1 and being inverted
>    to 0 due to Active Low in the descriptor flags;
> 5/ 0, i.e. electrically low signal, comes out from the SoC (compare
>    with 0/ above).
> 
> If it's not, we need to fix a root cause of it.
> 
> > Also we discussed here about using IoRestrictionNone/IoRestrictionNonePreserve as a potential solution to 
> > this problem, but this is a pure output pin, so that didn't seem right to us either.
> > 
> > In the end the main question, no matter the use case,  is how an active low pin, that's being 
> > asserted from BIOS, should be configured in the DSDT to be correctly represented by the code.
> > The patch was the result of not finding any solution to the problem above. Speaking strictly of the 
> > patch it should solve the problem of this case of active-low pins. 

> P.S. Before we are going further we need to see the dmesg when
> CONFIG_DEBUG_GPIO is set along with GpioIo() macro and corresponding
> _DSD() excerpts from DSDT.

You can send it privately if something is not okay to share (though I don't see
such in this case).

-- 
With Best Regards,
Andy Shevchenko