linux-kernel - Re: [PATCH 3/4] USB: serial: ftdi

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Date:   Mon, 7 Dec 2020 15:29:01 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-usb@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Johan Hovold <johan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        kernel-team@...roid.com
Subject: Re: [PATCH 3/4] USB: serial: ftdi_sio: Log the CBUS GPIO validity

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@...aro.org>
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> ---
>  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.

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.

>  	return 0;
>  }

Johan