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

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Date:	Mon, 10 Oct 2011 23:10:57 +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 03:55:30PM -0400, Alan Stern wrote:
> On Mon, 10 Oct 2011, Felipe Balbi wrote:
> 
> > On Mon, Oct 10, 2011 at 11:19:43AM -0400, Alan Stern wrote:
> > > On Mon, 10 Oct 2011, Felipe Balbi wrote:
> > > 
> > > > > > do we have sibling structures today? I dont think so.
> > > > > 
> > > > > no we don't.
> > > > 
> > > > Ok, here's a first shot at it:
> > > 
> > > 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 ?

ps: the best picture is on TI's OMAP4430 TRM (it's publicly available
from TI's website). So, if you want a better rendering of the
integration model, take a look at chapter 23.

-- 
balbi

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