linux-kernel - Re: [PATCH v5 05/10] gpiolib: Add gpio_property_name

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Message-ID: <CAGXv+5H0eGEjQU8qbKjua5qfbL2FaX2bMSyQg0PMVQrFfaiR8g@mail.gmail.com>
Date: Fri, 23 Aug 2024 15:50:55 +0800
From: Chen-Yu Tsai <wenst@...omium.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Rob Herring <robh@...nel.org>, Saravana Kannan <saravanak@...gle.com>, 
	Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, Wolfram Sang <wsa@...nel.org>, 
	Benson Leung <bleung@...omium.org>, Tzung-Bi Shih <tzungbi@...nel.org>, 
	Mark Brown <broonie@...nel.org>, Liam Girdwood <lgirdwood@...il.com>, 
	chrome-platform@...ts.linux.dev, devicetree@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, Douglas Anderson <dianders@...omium.org>, 
	Johan Hovold <johan@...nel.org>, Jiri Kosina <jikos@...nel.org>, linux-i2c@...r.kernel.org
Subject: Re: [PATCH v5 05/10] gpiolib: Add gpio_property_name_length()

On Thu, Aug 22, 2024 at 10:37 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Thu, Aug 22, 2024 at 05:19:58PM +0800, Chen-Yu Tsai wrote:
> > The I2C device tree component prober needs to get and toggle GPIO lines
> > for the components it intends to probe. These components may not use the
> > same name for their GPIO lines, so the prober must go through the device
> > tree, check each property to see it is a GPIO property, and get the GPIO
> > line.
> >
> > Instead of duplicating the GPIO suffixes, or exporting them to the
> > prober to do pattern matching, simply add and export a new function that
> > does the pattern matching and returns the length of the GPIO name. The
> > caller can then use that to copy out the name if it needs to.
>
> ...
>
> > +/**
> > + * gpio_property_name_length - Returns the GPIO name length from a property name
> > + * @str:     string to check
>
> It's property name, so, I would name this 'propname'.

Ack.

> > + * This function checks if the given name matches the GPIO property patterns, and
> > + * returns the length of the name of the GPIO. The pattern is "*-<GPIO suffix>"
> > + * or just "<GPIO suffix>".
> > + *
> > + * Returns:
> > + * The length of the string before '-' if it matches "*-<GPIO suffix>", or
>
> What about "x-y-gpios"? It's unclear what will be the behaviour.

I thought it was implied that the '-' mentioned here is the one before the
suffix. I made it more explicit.

> > + * 0 if no name part, just the suffix, or
> > + * -EINVAL if the string doesn't match the pattern.
> > + */
> > +int gpio_property_name_length(const char *str)
>
> gpio_get_... ?

Ack.

> > +{
> > +     size_t len;
> > +
> > +     len = strlen(str);
>
> If it has a thousands characters...?

Shouldn't matter much? I suppose using strrchr() as you suggested
requires one less pass.

> > +     /* string need to be at minimum len(gpio) */
> > +     if (len < 4)
> > +             return -EINVAL;
>
> Do we really need it here? See below as well.
>
> > +     /* Check for no-name case: "gpio" / "gpios" */
> > +     for (const char *const *p = gpio_suffixes; *p; p++)
> > +             if (!strcmp(str, *p))
> > +                     return 0;
>
> > +     for (size_t i = len - 4; i > 0; i--) {
> > +             /* find right-most '-' and check if remainder matches suffix */
> > +             if (str[i] != '-')
> > +                     continue;
> > +
> > +             for (const char *const *p = gpio_suffixes; *p; p++)
> > +                     if (!strcmp(str + i + 1, *p))
> > +                             return i;
> > +
> > +             return -EINVAL;
> > +     }
>
> This can be combined with the above
>
>         for (const char *const *p = gpio_suffixes; *p; p++) {
>                 /*
>                  * Find right-most '-' and check if remainder matches suffix.
>                  * If no separator found, check for no-name cases.
>                  */
>                 dash = strrchr(propname, '-');

I believe this line could be moved out of the for-loop. Otherwise it
looks much more concise compared to my version. I'll omit the comment
though, as it is just rehashing the kerneldoc description, and now
that the function is so short, it shouldn't be hard to read.

I'll add you as "Suggested-by".


Thanks
ChenYu

>                 if (!strcmp(dash ? dash + 1 : propname, *p))
>                         return i;
>         }
>
> > +     return -EINVAL;
> > +}
>
> --
> With Best Regards,
> Andy Shevchenko
>
>