linux-kernel - Re: [PATCH] MIPS: pci: lantiq: restore reset gpio polarity

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Message-ID: <ZmnA-fifJkEBt0lH@google.com>
Date: Wed, 12 Jun 2024 08:38:33 -0700
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc: Martin Schiller <ms@....tdt.de>, hauke@...ke-m.de,
	rdunlap@...radead.org, robh@...nel.org, bhelgaas@...gle.com,
	linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] MIPS: pci: lantiq: restore reset gpio polarity

Hi Thomas, Martin,

On Tue, Jun 11, 2024 at 04:12:18PM +0200, Thomas Bogendoerfer wrote:
> On Fri, Jun 07, 2024 at 11:04:00AM +0200, Martin Schiller wrote:
> > Commit 90c2d2eb7ab5 ("MIPS: pci: lantiq: switch to using gpiod API") not
> > only switched to the gpiod API, but also inverted / changed the polarity
> > of the GPIO.
> > 
> > According to the PCI specification, the RST# pin is an active-low
> > signal. However, most of the device trees that have been widely used for
> > a long time (mainly in the openWrt project) define this GPIO as
> > active-high and the old driver code inverted the signal internally.
> > 
> > Apparently there are actually boards where the reset gpio must be
> > operated inverted. For this reason, we cannot use the GPIOD_OUT_LOW/HIGH
> > flag for initialization. Instead, we must explicitly set the gpio to
> > value 1 in order to take into account any "GPIO_ACTIVE_LOW" flag that
> > may have been set.
> > 
> > In order to remain compatible with all these existing device trees, we
> > should therefore keep the logic as it was before the commit.
> > 
> > Fixes: 90c2d2eb7ab5 ("MIPS: pci: lantiq: switch to using gpiod API")
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Martin Schiller <ms@....tdt.de>
> > ---
> >  arch/mips/pci/pci-lantiq.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> applied to mips-fixes

The patch is unfortunately also wrong as it will break any board that
actually has correct polarity annotation.

I will prepare a quirk for drivers/gpio/gpiolib-of.c to force the
polarity to low for this GPIO.

Thanks.

-- 
Dmitry