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

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Date:   Mon, 07 Dec 2020 15:00:37 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Johan Hovold <johan@...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>,
        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 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@...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.

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...