netdev - Re: [PATCH] cdc_ncm: do not call usbnet_link_change from cdc_ncm

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Date:	Tue, 08 Mar 2016 20:37:08 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Bjørn Mork <bjorn@...k.no>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	David Miller <davem@...emloft.net>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Oliver Neukum <oneukum@...e.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	USB list <linux-usb@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH] cdc_ncm: do not call usbnet_link_change from
 cdc_ncm_bind

On Tue, 2016-03-08 at 21:18 +0100, Bjørn Mork wrote:
> Linus Torvalds <torvalds@...ux-foundation.org> writes:
> 
> > 
> > So looking at this, I wonder...
> > 
> > Why is that FLAG_LINK_INTR thing not just always used?
> > 
> > The _only_ thing that FLAG_LINK_INTR does is to cause
> > 
> >         usbnet_link_change(dev, 0, 0);
> > 
> > to be called after network device attach. That doesn't seem to be controversial.
> Not all usbnet drivers support carrier detection, which is required to
> ever bring the link up again.
> 
> > 
> > Looking at some examples, we have ax88179_178a.c that doesn't set the
> > flag, but instead does that usbnet_link_change() call at the end of
> > ax88179_bind().
> > 
> > There are a few drivers that seem to never call that
> > usbnet_link_change() at all, and don't have that FLAG_LINK_INTR flag.
> > Would they break?
> Yes.  Drivers without carrier detection will be "down" forever.
> 
> > 
> > Why is it called "FLAG_LINK_INTR" anyway? There doesn't seem to be
> > anything "INTR" about it.
> Beats me.  I can only say that I always find naming difficult...
> We could ask Ben, who introduced it in:
[...]

It is supposed to imply that the device generates link-change
interrupts.  Of course it is also possible for a device driver to
satisfy the requirement by polling the link state.

Ben.

-- 
Ben Hutchings
Sturgeon's Law: Ninety percent of everything is crap.
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