Re: [PATCH 2/2] USB: serial: cp210x: add gpio-configuration debug printk

Johan Hovold
2021-04-09T16:32:54Z

On Fri, Apr 09, 2021 at 07:22:26PM +0300, Andy Shevchenko wrote:
> On Fri, Apr 9, 2021 at 6:52 PM Johan Hovold <johan@kernel.org> wrote:
> >
> > Add a debug printk to dump the GPIO configuration stored in EEPROM
> > during probe.
> >
> > Signed-off-by: Johan Hovold <johan@kernel.org>
> > ---
> > drivers/usb/serial/cp210x.c | 6 ++++++
> > 1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
> > index ceb3a656a075..ee595d1bea0a 100644
> > --- a/drivers/usb/serial/cp210x.c
> > +++ b/drivers/usb/serial/cp210x.c
> > @@ -1543,10 +1543,16 @@ static int cp210x_gpio_init_valid_mask(struct gpio_chip *gc,
> > {
> > struct usb_serial *serial = gpiochip_get_data(gc);
> > struct cp210x_serial_private *priv = usb_get_serial_data(serial);
> > + struct device *dev = &serial->interface->dev;
> > unsigned long altfunc_mask = priv->gpio_altfunc;
> >
> > bitmap_complement(valid_mask, &altfunc_mask, ngpios);
> >
> > + if (bitmap_empty(valid_mask, ngpios))
> > + dev_dbg(dev, "no pin configured for GPIO\n");
>
> Shouldn't we drop the GPIO device completely in such a case?

I considered it when we first added support for GPIOs to this driver but
decided not to. The reason being that we want to to tell user-space that
the device has gpio capability even if the GPIOs are currently muxed (in
EEPROM) for other functionality.

> Bart, wouldn't it be a good idea for GPIO library to do something like
> this on driver's behalf?

I'd say this is mostly useful for hotpluggable devices with EEPROM
configuration and is probably best handled by the drivers.

> > + else
> > + dev_dbg(dev, "GPIO.%*pbl configured for GPIO\n", ngpios,
> > + valid_mask);
>
> A nit-pick:
> I would change GPIO -> pin in the second message in the first occurrence.

"GPIO.n" are the actual pin names from the datasheet (cf. ftdi_sio which
use "CBUSn" here). It's just a debug statement anyway.

Johan