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

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Date:   Wed, 16 Dec 2020 11:53:57 -0800
From:   Drew Fustini <drew@...gleboard.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] gpiolib: Allow name duplicates of "" and "NC"

On Tue, Dec 15, 2020 at 09:03:08AM -0800, Bjorn Andersson 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 am the one who added the gpio line names to the am335x dts board
files, and I am happy to change them if it will make unique line name
logic simpler.

I used the notation of "[<non-gpio-functionality>]" to make it easy for
the user to realize that the corresponding gpiolines could not be used
on these boards (BeagleBone and PocketBeagle) for actual GPIO.  I used
generic names like "[ethernet]" because I didn't think it made sense
to confuse the user by using the precise name of the non-gpio function
(such as "[gmii1_rxd0]").  I could post a patch for the dts files that
restores unique names for "[ethernet]", "[emmc"], "[i2c0]",
"[SYSBOOT]" and "[JTAG]".

As for "[NC]", the BGA balls corresponding to these gpio lines are
simply not connected to any circuits on the board.  I happy to change
that to whatever name people prefer for a non-connected pin ("", "NC",
etc).

Thanks,
Drew