linux-kernel - RE: [PATCH 1/2] usb: configfs: allow UDC binding rule configured as binding to *any* UDC

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Date:	Thu, 5 May 2016 05:46:39 +0000
From:	"Du, Changbin" <changbin.du@...el.com>
To:	Krzysztof Opasiak <k.opasiak@...sung.com>,
	"balbi@...nel.org" <balbi@...nel.org>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"corbet@....net" <corbet@....net>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Du, Changbin" <changbin.du@...il.com>,
	"Du@...r.kernel.org" <Du@...r.kernel.org>
Subject: RE: [PATCH 1/2] usb: configfs: allow UDC binding rule configured as
 binding to *any* UDC

Hi,
> > On most platforms, there is only one device controller available.
> > In this case, we desn't care the UDC's name. So let's ignore the
> > name by setting 'UDC' to 'any'.
> 
> Hmm libubsgx allows to do this for a very long time. You simply pass
> NULL instead of pointer to usbg_udc.
> 
> It is also possible to do this from command line, just simply:
> 
> $ echo `ls -1 /sys/class/udc | head -n 1` > UDC
> 
> So if we can easily do this from user space what's the benefit of adding
> this special "any" keyword to kernel?
> 
Well, it is just for *easy to use*. Looking up /sys/class/udc mostly
can be skipped. The UDC core support this convenience behavior, 
so why don't we export it with a little change?

> > And also we can change UDC name
> > at any time if it is not binded (no need set to "" first).
> >
> 
> Not sure if:
> 
> $ echo "" > UDC
> 
> is really a problem. Personally I'm quite used to situation in which I
> have to turn the light off before turning it on once again;)
> 
That is not a problem. But just avoid pseudo 'busy'. If gadget is not 
bind, it is free to reconfigure it. So seem no need block re-configuration.

In a word, this patch is just an improvement, not to fix any issues or
add new function.

> Cheers,
> --
> Krzysztof Opasiak
> Samsung R&D Institute Poland
> Samsung Electronics

Thanks,
Du, Changbin