linux-kernel - Re: [PATCH] usb: move usb_calc_bus

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Date:	Fri, 19 Feb 2016 14:48:50 -0800
From:	Doug Anderson <dianders@...omium.org>
To:	Alan Stern <stern@...land.harvard.edu>,
	John Youn <John.Youn@...opsys.com>,
	Felipe Balbi <balbi@...nel.org>, Arnd Bergmann <arnd@...db.de>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Heiko Stuebner <heiko@...ech.de>,
	Stefan Wahren <stefan.wahren@...e.com>,
	Felipe Balbi <balbi@...com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: move usb_calc_bus_time into common code

Hi,

On Fri, Feb 19, 2016 at 1:52 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Fri, 19 Feb 2016, Arnd Bergmann wrote:
>
>> The dwc2 dual-role USB controller driver has started calling
>> usb_calc_bus_time, and does so regardless of whether it is
>> being built as a host controller or gadget. In case all
>
> Out of curiosity...  Why does dwc2 need to calculate bus times when it
> is in device mode?

Hoo boy.  it doesn't.  Nor does it need to properly set the even/odd
frame in device mode.

Basically dwc2's "core.c" has a whole bunch of stuff in it that's host
only and isn't guarded with any #ifdef.  ...yet that file is included
in gadget-only builds.  It's a bit of a mess.  Take a gander at all of
the "dwc2_hc_xxx" functions sitting in "drivers/usb/dwc2/core.c".

Long term that needs to be cleaned up, but such a cleanup is going to
be a bit of churn so we'd need to schedule it for a time when not much
else is going on (and presumably it should be done by John or in close
coordination with him so it can get Acked / landed quickly to avoid
conflicts?).  To do this we'd have to figure out why some things are
in "core.c" and some in "hcd.c" and if it makes sense to move them all
to "hcd.c" or if we need a new "core_hc.c" or something...  All of
that design predates me.

In any case I guess we need a solution for right now, huh?

One terribly lame hack would be to just make a dummy no-op
"dwc2_hc_set_even_odd_frame()" if host mode is disabled.  That doesn't
really fix the root problem of lots of host mode code being compiled
in a gadget-only driver.  It also adds an ugly "#ifdef".  ...but it
does get around the current compile error.

What do folks think?

-Doug