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

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Message-ID: <X9pUjU6hPI1cKS3H@builder.lan>
Date:   Wed, 16 Dec 2020 12:40:13 -0600
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        MSM <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH] gpiolib: Allow name duplicates of "" and "NC"

On Wed 16 Dec 06:46 CST 2020, Linus Walleij 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.
> 
> I pushed this patch yesterday that fixes the obvious "(empty string)" problem:
> https://lore.kernel.org/linux-gpio/20201215123755.438369-1-linus.walleij@linaro.org/T/#u
> 

Unfortunately we've almost consistently used "NC" for the Qualcomm
platforms, so that seems to fix only a single platform :(

> But I see this is for device tree line naming only, right?
> 

Yes.

> I think I will conjure a patch allowing identical naming only for
> device property naming (like from device tree) but emitting a
> warning so that people fix it to something unique moving
> forward.
> 

I'm not against emitting a dev_err() when we hit duplicates, remove the
return and then update the various dts files to use "" for things that
doesn't have a name.

Regarding special handling of the DT case, I think (beyond making all
these boards boot again) it would be nice to make
gpiochip_set_desc_names() take the list of names and a length and use
the same function in both code paths...


PS. strlen(names[i]) is O(N), strcmp(names[i], "") is O(1).

Regards,
Bjorn