linux-kernel - Re: [PATCH] gpiolib: Allow name duplicates of "" and "NC"

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Date:   Tue, 15 Dec 2020 11:59:29 -0600
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        linux-gpio <linux-gpio@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] gpiolib: Allow name duplicates of "" and "NC"

On Tue 15 Dec 11:42 CST 2020, Bartosz Golaszewski wrote:

> On Tue, Dec 15, 2020 at 6:02 PM Bjorn Andersson
> <bjorn.andersson@...aro.org> wrote:
> >
> > Not all GPIO pins are exposed to the world and this is typically
> > described by not giving these lines particular names, commonly "" or
> > "NC".
> >
> > With the recent introduction of '2cd64ae98f35 ("gpiolib: Disallow
> > identical line names in the same chip")' any gpiochip with multiple such
> > pins will refuse to probe.
> >
> > Fix this by treating "" and "NC" as "no name specified" in
> > gpio_name_to_desc()
> >
> > Fixes: 2cd64ae98f35 ("gpiolib: Disallow identical line names in the same chip")
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> > ---
> >
> > The introduction of 2cd64ae98f35 breaks pretty much all Qualcomm boards and
> > grepping the DT tree indicates that other vendors will have the same problem.
> >
> > In addition to this the am335x-* boards will also needs "[NC]", "[ethernet]",
> > "[emmc"], "[i2c0]", "[SYSBOOT]" and "[JTAG]" added to this list to allow
> > booting v5.11 with the past and present dtb/dts files.
> >
> >  drivers/gpio/gpiolib.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> > index b3340ba68471..407ba79ae571 100644
> > --- a/drivers/gpio/gpiolib.c
> > +++ b/drivers/gpio/gpiolib.c
> > @@ -302,7 +302,7 @@ static struct gpio_desc *gpio_name_to_desc(const char * const name)
> >         struct gpio_device *gdev;
> >         unsigned long flags;
> >
> > -       if (!name)
> > +       if (!name || !strcmp(name, "") || !strcmp(name, "NC"))
> >                 return NULL;
> >
> >         spin_lock_irqsave(&gpio_lock, flags);
> > --
> > 2.29.2
> >
> 
> I have a bad feeling about this. This opens the door for all kinds of
> exceptions: "N/A", "none" etc. Depending on whose boards are getting
> broken.
> 
> If non-uniqueness of names is needed then let's better revert 2cd64ae98f35.
> 

I like the intent of 2cd64ae98f35, but even if we decide what the
"unconnected" name should be we have a slew of boards that won't boot
v5.11-rc1 (or with any pre-v5.11 DTBs).

As such I think we need to revert the "return -EEXIST" part of the
patch.


Looking forward perhaps we should define "" to be the "not a gpio"-name,
revise my patch and fix up the DTs accordingly? And keep the dev_err()
as it currently is?

Regards,
Bjorn