linux-kernel - Re: [PATCH 1/5 v13] arm: omap: usb: ehci and ohci hwmod structures for omap4

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Date:	Tue, 11 Oct 2011 10:04:28 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Felipe Balbi <balbi@...com>
cc:	"Munegowda, Keshava" <keshava_mgowda@...com>,
	Paul Walmsley <paul@...an.com>, <linux-usb@...r.kernel.org>,
	<linux-omap@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<khilman@...com>, <b-cousson@...com>, <gadiyar@...com>,
	<sameo@...ux.intel.com>, <parthab@...ia.ti.com>,
	<tony@...mide.com>, <johnstul@...ibm.com>, <vishwanath.bs@...com>,
	Greg KH <greg@...ah.com>
Subject: Re: [PATCH 1/5 v13] arm: omap: usb: ehci and ohci hwmod structures
 for omap4

On Tue, 11 Oct 2011, Felipe Balbi wrote:

> > > It doesn't shown here, but the TLL link is completely optional. It's
> > > mainly used for modem integration, IIRC. Still, if we're using TLL, EHCI
> > > and OHCI will depend on a clock provided by the USBTLL block.
> > > 
> > > Clearly, USBTLL isn't either a parent of UHH, nor a parent of EHCI/OHCI
> > > blocks. We can, from a code perspective, make USBTLL into a parent of
> > > UHH to make things simpler, but this will mean that calling
> > > pm_runtime_get() will also unconditionaly turn on TLL clock, unless we
> > > add some nasty hacks to allow TLL know if *HCI port is in TLL mode.
> > > 
> > > That's why I decided for making TLL and UHH siblings, because that's a
> > > closer relationship than parent-child.
> > > 
> > > Can you see the problem now ?
> > 
> > Okay, now I understand better.  The word "sibling" implies that the two 
> > objects have the same parent, so a different word would describe this 
> > relationship better.  Something like "friend" or "associate".
> > 
> > Or maybe, following Paul's suggestion, the driver core doesn't have to 
> > be changed at all.
> 
> I see... I just thought that if there are other similar cases, it might
> make sense to have a more generic way to make those two devices talk to
> each other. But if you all agree that an EXPORT_SYMBOL_GPL() is enough,
> then it's ok ;-)

At the moment, I can't see any way to set up a more generic mechanism 
that wouldn't be more complicated and have higher overhead than a 
simple EXPORT_SYMBOL_GPL.

Can this be handled by adding another resource to a platform_device?  
That at least would make use of an already-existing mechanism.

Alan Stern

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