linux-kernel - Re: [PATCH v2 4/9] gpio: regmap: add the .fixed_direction

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Message-ID: <CAMRc=Mf7bnAM=-A4jWrqOvS8-ZetTHPfMaEpmQdbKMt6SWKtQQ@mail.gmail.com>
Date: Tue, 16 Sep 2025 05:52:31 -0400
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Michael Walle <mwalle@...nel.org>
Cc: Frank Li <Frank.Li@....com>, Ioana Ciornei <ioana.ciornei@....com>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Linus Walleij <linus.walleij@...aro.org>, Bartosz Golaszewski <brgl@...ev.pl>, 
	Shawn Guo <shawnguo@...nel.org>, Lee Jones <lee@...nel.org>, devicetree@...r.kernel.org, 
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/9] gpio: regmap: add the .fixed_direction_output
 configuration parameter

On Mon, 15 Sep 2025 14:45:58 +0200, Michael Walle <mwalle@...nel.org> said:
> Hi Ioana,
>
> On Mon Sep 15, 2025 at 2:23 PM CEST, Ioana Ciornei wrote:
>> There are GPIO controllers such as the one present in the LX2160ARDB
>> QIXIS FPGA which have fixed-direction input and output GPIO lines mixed
>> together in a single register. This cannot be modeled using the
>> gpio-regmap as-is since there is no way to present the true direction of
>> a GPIO line.
>>
>> In order to make this use case possible, add a new configuration
>> parameter - fixed_direction_output - into the gpio_regmap_config
>> structure. This will enable user drivers to provide a bitmap that
>> represents the fixed direction of the GPIO lines.
>
> I wonder about the ownership of that allocated memory in the config
> structure (and btw, I guess you leak the memory in your driver) and
> if it's not better and more error proof to allocate and copy the
> bitmap in gpio-regmap too (and maybe use devm_bitmap_alloc()) and
> leave it to the caller to handle the passed bitmap. I.e. it could
> also be on the stack.
>

I was under the impression that whatever is in the config structure for GPIO
regmap init function is only required to stay alive until that call returns?

If so, then yes, a deep copy of everything from this structure is required.

> Otherwise, this looks good.
>

[snip]

>>
>> +	if (offset >= chip->ngpio)
>> +		return -EINVAL;
>
> Not sure this can happen. I tried to look into gpiolib.c but
> couldn't find anything obvious that it can't happen. Maybe Linus or
> Bartosz can comment on that.
>

Indeed, this is handed by GPIO core, please drop it.

[snip]

Bartosz