Re: [PATCH 3/4] USB: serial: ftdi_sio: Log the CBUS GPIO validity

[Marc Zyngier]

On 2020-12-07 14:29, Johan Hovold wrote:
> On Fri, Dec 04, 2020 at 04:47:38PM +0000, Marc Zyngier wrote:
> > The validity of the ftdi CBUS GPIO is pretty hidden so far,
> > and finding out *why* some GPIOs don't work is sometimes
> > hard to identify. So let's help the user by displaying the
> > map of the CBUS pins that are valid for a GPIO.
> >
> > Also, tell the user about the magic ftx-prog tool that can
> > make GPIOs appear: https://github.com/richardeoin/ftx-prog
> >
> > Suggested-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> > Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> > ---
> >  drivers/usb/serial/ftdi_sio.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/drivers/usb/serial/ftdi_sio.c 
> > b/drivers/usb/serial/ftdi_sio.c
> > index 13e575f16bcd..b9d3b33891fc 100644
> > --- a/drivers/usb/serial/ftdi_sio.c
> > +++ b/drivers/usb/serial/ftdi_sio.c
> > @@ -2012,6 +2012,15 @@ static int ftdi_gpio_init_valid_mask(struct 
> > gpio_chip *gc,
> >
> >  	bitmap_complement(valid_mask, &map, ngpios);
> >
> > +	if (bitmap_empty(valid_mask, ngpios))
> > +		dev_warn(&port->dev, "No usable GPIO\n");
>
> This isn't an error of any kind, and certainly not something that
> deserves a warning in the system log on every probe. Not everyone cares
> about the GPIO interface.
>
> > +	else
> > +		dev_info(&port->dev, "Enabling CBUS%*pbl for GPIO\n",
> > +			 ngpios, valid_mask);
>
> And while printing this mask has some worth I'm still reluctant to be
> spamming the logs with it. Just like gpolib has a dev_dbg() for
> registering chips, this should probably be demoted to KERN_DEBUG as
> well.
>
> > +
> > +	if (!bitmap_full(valid_mask, ngpios))
> > +		dev_warn_once(&port->dev, "Consider using a tool such as ftx-prog 
> > to enable GPIOs if required\n");
> > +
>
> And again, this is not something that belongs in the logs of just about
> every system with an attached ftdi device.

Fine by me, this patch can be dropped without issue. After all,
I now know how to deal with these chips.

> While not possible to combine with the valid_mask approach, this is
> something which we could otherwise add to the request() callback for 
> the
> first request that fails due to the mux configuration.

That was Linus' initial suggestion. But I think a consistent user
API is more important than free advise in the kernel log.

Thanks,

        M.
--
Jazz is not dead. It just smells funny...