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 17:08:40 +0300
From:	Felipe Balbi <balbi@...com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Felipe Balbi <balbi@...com>,
	"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

Hi,

On Tue, Oct 11, 2011 at 10:04:28AM -0400, Alan Stern wrote:
> 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.

maybe, but let's go with EXPORT_SYMBOL_GPL(). My only concern is that
this IP comes from synopsys, and I'm not really keen on adding
OMAP-specific, integration-related knowledge on a driver which was
supposed to be reusable ;-)

But at least for the time being, I guess that's what we need to do ;-)

tks

-- 
balbi

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