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 11:13:53 +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 Mon, Oct 10, 2011 at 08:15:29PM -0400, Alan Stern wrote:
> > > > > In fact we do already have sibling lists.  They are maintained as part 
> > > > > of the device_private structure.  What we are missing is a 
> > > > > device_for_each_sibling() routine.  It could be added pretty easily; it 
> > > > > would be similar to device_for_each_child().
> > > > 
> > > > care to point out where is ?
> > > > 
> > > > 68 struct device_private {
> > > > 69         struct klist klist_children;
> > > > 70         struct klist_node knode_parent;
> > > -------------^  Here.  The "parent" in the name refers to where the
> > >                 head of the list is stored.
> > > 
> > > > 71         struct klist_node knode_driver;
> > > > 72         struct klist_node knode_bus;
> > > > 73         void *driver_data;
> > > > 74         struct device *device;
> > > > 75 };
> > > 
> > > From device_add():
> > > 
> > > 	if (parent)
> > > 		klist_add_tail(&dev->p->knode_parent,
> > > 			       &parent->p->klist_children);
> > 
> > that's a parent -> child relationship. What we have on this case is:
> > 
> >  --------------                ---------------
> > |              |              |               |          |\
> > |   UHH        |  clocks, etc |    USBTLL     |          | |
> > |              | <==========> |               | <======> | | <====> ports
> > |     -------  |              | (Transceiver- |          | |
> > |    |  EHCI | |              | less Link)    |          |/
> > |     -------  |              |               |         Port MUX
> > |              |              |               |
> > |     -------  |              |               |
> > |    |  OHCI | |              |               |
> > |     -------  |              |               |
> > |              |              |               |
> >  --------------                ---------------
> > 
> > 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 ;-)

thanks

-- 
balbi

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