Hi Uwe,

On Mon, Mar 6, 2017 at 10:30 AM, Uwe Kleine-K?nig
[off-list ref] wrote:

On Mon, Mar 06, 2017 at 10:09:50AM +0100, Geert Uytterhoeven wrote:

quoted

On Mon, Mar 6, 2017 at 9:58 AM, Uwe Kleine-K?nig
[off-list ref] wrote:

quoted

On Mon, Mar 06, 2017 at 09:49:39AM +0100, Geert Uytterhoeven wrote:

quoted

quoted

Given that mctrl-gpio can be useful on legacy platforms, a device could
silently run without cts-gpio even there.

On platforms were CONFIG_GPIOLIB=n, this is not true, so the issue is moot.

All serial drivers using (optional) mctrl-gpio have this in Kconfig:

    select SERIAL_MCTRL_GPIO if GPIOLIB

So they will use mctrl-gpio when GPIOLIB is enabled.
If GPIOPLIB is disabled, no flow control GPIOs are expected, and the
driver should not break that case.

So it all boils down to the question: Is GPIOLIB=n enough to assume no
gpio is needed?

I'd say it is not.

How does the platform register these GPIOs when GPIOPLIB is not enabled by
the platform, and gpiod_add_lookup_table() is thus not available?

Obviously the platformcode cannot. In this case you could argue that
platformcode shouldn't register the device if a gpio is necessary. But
this reasoning doesn't work for (DT=y || ACPI=y) && GPIOLIB=n.

I wouldn't want to code this in each driver (something like:

        if (IS_ENABLED(GPIOLIB) || device_is_instantiated_by_dt(dev) || device_is_instantiated_by_acpi(dev))
                gpios = mctrl_gpio_init(...);
        else
                gpios = NULL;

). Putting this into GPIOLIB is the right approach, and so this is
another argument for HALFGPIOLIB. This would fix mctrl_gpio_init en
passant.

Do we have platforms where DT=y || ACPI=y, but GPIOLIB=n?
Ah, x86 ;-)

Anyway, for sh-sci.c, platforms either have DT and GPIOLIB, or they do not
need mctrl-gpio.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds