Re: [PATCH v10 1/1] USB: serial: cp210x: Adding GPIO support for CP2105

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Wed, Oct 26, 2016 at 11:09 AM, Johan Hovold <johan@xxxxxxxxxx> wrote:
> On Tue, Oct 25, 2016 at 11:34:40AM +0200, Linus Walleij wrote:

>> I was thinking on either reusing the .names field of the
>> struct gpiochip to name the lines for the userspace
>> chardev. With the sideeffect of the names getting reflected
>> also to sysfs if using that.
>
> Simply reusing .names would cause problems since the old sysfs name
> space is flat, so you would be unable to use more than one pluggable
> expander (unless also encoding the topology in the name).

Hm it seems we should actually #ifdef that field for sysfs then,
it has no applicability outside the legacy sysfs.

> Providing default names from the driver could perhaps be useful at
> times. For this particular chip the names would still be GPIO_0, GPIO_1
> and GPIO_2 (possibly with a suffix depending on which of the two
> controllers they hang off of) however, which may not be much better than
> using chip->base + offset. I'd assume this to be the common case.

The chardev names are pertaining to a certain device like
"gpiochip1" already so the names only need to be unique
per-instance.

If we made them globally unique we could just use the .names
in gpiochip anyways, but that seems ugly.

What about suppling

gpiochip_set_names(struct gpio_chip *gc,
                               char **names);

As the size of the array is implicit from ngpios and the function
would be kernel-internal anyways.

> Device-tree overlays is what I see a real use for where different
> overlays can be applied based on topology data to describe what is
> actually connected to a pin in a specific setup. And that seems like
> something that could be useful for normal (static) DT systems as well
> (e.g. describe what's actually connected to those Beaglebone pins).

Yeah these overlays ... discussed that a lot recently.
It fits the Beaglebone indeed.

Yours,
Linus Walleij
--
To unsubscribe from this list: send the line "unsubscribe linux-gpio" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html