[PATCH RESEND v2 2/2] usb: udc: Try to clarify an error message

[Marek Vasut]

On 10/2/23 15:46, Miquel Raynal wrote:
> At some point when trying to use USB gadgets, two situations may arise
> and lead to a failure. Either the UDC (USB Device Controller) is not
> available at all (not described or not probed) or the UDC is already in
> use. For instance, as the USB Ethernet gadget remains bound to the UDC,
> the use of any other USB gadget (fastboot, dfu, etc) *after* will always
> fail with the "couldn't find an available UDC" error.
> 
> Let's give a more helpful message by making a difference between the two
> cases. Let's also hint people who would get this error and grep it into
> the sources a better explanation of what's wrong with their workflow.
> 
> Signed-off-by: Miquel Raynal <miquel.raynal at bootlin.com>
> ---
> While doing this I really wanted to add "much more" error comments but I
> faced another reality: often the messages are there but use
> pr_err/log_err which is actually silenced by default with LOGLEVEL=3, so
> I consider this unnecessary, as decreasing the loglevel will make these
> messages appear. I would have expected errors to be displayed, but I
> understand it makes the binaries even bigger.
> 
> Resend: no change.
> 
> Changes in v2:
> * s/UDC/UDCs/. I kept the sentence as it was as the suggested form did
>    not sound well at all when there is only one UDC.
> ---
>   drivers/usb/gadget/udc/udc-core.c | 13 ++++++++++++-
>   1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/gadget/udc/udc-core.c b/drivers/usb/gadget/udc/udc-core.c
> index 7f73926cb3e..8405b03462e 100644
> --- a/drivers/usb/gadget/udc/udc-core.c
> +++ b/drivers/usb/gadget/udc/udc-core.c
> @@ -323,6 +323,7 @@ err1:
>   int usb_gadget_probe_driver(struct usb_gadget_driver *driver)
>   {
>   	struct usb_udc		*udc = NULL;
> +	unsigned int		udc_count = 0;
>   	int			ret;
>   
>   	if (!driver || !driver->bind || !driver->setup)
> @@ -330,12 +331,22 @@ int usb_gadget_probe_driver(struct usb_gadget_driver *driver)
>   
>   	mutex_lock(&udc_lock);
>   	list_for_each_entry(udc, &udc_list, list) {
> +		udc_count++;
> +
>   		/* For now we take the first one */
>   		if (!udc->driver)
>   			goto found;
>   	}
>   
> -	printf("couldn't find an available UDC\n");
> +	if (!udc_count)
> +		printf("No UDC available in the system\n");
> +	else
> +		/* When this happens, users should 'unbind <class> <index>'
> +		 * using the output of 'dm tree' and looking at the line right
> +		 * after the USB peripheral/device controller.
> +		 */
> +		printf("All UDCs in use (%d available), use the unbind command\n",
> +		       udc_count);

Users should really use 'bind' command in the first place, to avoid this 
guesswork to which UDC (on systems with multiple UDCs) a gadget gets 
bound to, and instead bind the gadget to specific UDC they want to bind 
it to. This code should then be removed entirely.