Re: [PATCH v3 1/6] drivers: phy: add generic PHY framework

[Kishon Vijay Abraham I]

Hi,

On Friday 19 April 2013 02:39 PM, Grant Likely wrote:
> On Tue, 16 Apr 2013 15:48:07 +0530, Kishon Vijay Abraham I <kishon@xxxxxx> wrote:
> > On Tuesday 16 April 2013 01:20 AM, Grant Likely wrote:
> > > On Mon, 15 Apr 2013 17:56:10 +0530, Kishon Vijay Abraham I <kishon@xxxxxx> wrote:
> > > > On Monday 15 April 2013 05:04 PM, Grant Likely wrote:
> > > > > On Wed, 20 Mar 2013 14:42:00 +0530, Kishon Vijay Abraham I <kishon@xxxxxx> wrote:
> > > > We have decided not to implement the PHY layer as a separate bus layer.
> > > > The PHY provider can be part of any other bus. Making the PHY layer as a
> > > > bus will make the PHY provider to be part of multiple buses which will
> > > > lead to bad design. All we are trying to do here is keep the pool of PHY
> > > > devices under PHY class in this layer and help any controller that wants
> > > > to use the PHY to get it.
> > >
> > > If you're using a class, then you already have your list of registered
> > > phy devices! :-) No need to create another global list that you need to
> > > manage.
> >
> > right. We already use _class_dev_iter_ for finding the phy device.
> > .
> > .
> > +static struct phy *of_phy_lookup(struct device *dev, struct device_node
> > *node)
> > +{
> > +	struct phy *phy;
> > +	struct class_dev_iter iter;
> > +
> > +	class_dev_iter_init(&iter, phy_class, NULL, NULL);
> > +	while ((dev = class_dev_iter_next(&iter))) {
> > +		phy = container_of(dev, struct phy, dev);
> > +		if (node != phy->of_node)
> > +			continue;
> > +
> > +		class_dev_iter_exit(&iter);
> > +		return phy;
> > +	}
> > +
> > +	class_dev_iter_exit(&iter);
> > +	return ERR_PTR(-EPROBE_DEFER);
> > +}
> > .
> > .
> >
> > however we can't get rid of the other list (phy_bind_list) where we
> > maintain the phy binding information. It's used for the non-dt boot case.
>
> Why? If you're using a class, then it is always there. Why would non-DT
> and DT be different in this regard? (more below)
>
> > > > > Since there is at most a 1:N relationship between host controllers and
> > > > > PHYs, there shouldn't be any need for a separate structure to describe
> > > > > binding. Put the inding data into the struct phy itself. Each host
> > > > > controller can have a list of phys that it is bound to.
> > > >
> > > > No. Having the host controller to have a list of phys wont be a good
> > > > idea IMHO. The host controller is just an IP and the PHY to which it
> > > > will be connected can vary from board to board, platform to platform. So
> > > > ideally this binding should come from platform initialization code/dt data.
> > >
> > > That is not what I mean. I mean the host controller instance should
> > > contain a list of all the PHYs that are attached to it. There should not
> >
> > Doesn't sound correct IMO. The host controller instance need not know
> > anything about the PHY instances that is connected to it. Think of it
> > similar to regulator, the controller wouldn't know which regulator it is
> > connected to, all it has to know is it just has a regulator connected to
> > it. It's up-to the regulator framework to give the controller the
> > correct regulator. It's similar here. It makes sense for me to keep a
> > list in the PHY framework in order for it to return the correct PHY (but
> > note that this list is not needed for dt boot).
>
> With regulators and clocks it makes sense to have a global
> registration place becase both implement an interconnected network
> independent of the device that use them. (clocks depend on other clocks;
> regulators depend on other regulators).
>
> Phys are different. There is a 1:N relationship between host controllers
> and phys, and you don't get a interconnected network of PHYs. Its a bad
> idea to keep the binding data separate from the actual host controller
> when there is nothing else that actually needs to use the data. It
> creates a new set of data structures that need housekeeping to keep them
> in sync with the actual device structures. It really is just a bad idea
> and it becomes more difficult (in the non-DT case) to determine what
> data is associated with a given host controller. You can't tell by
> looking at the struct device.
>
> Instead, for the non-DT case, do what we've always done for describing
> connections. Put the phy reference into the host controllers
> platform_data structure.
hmm... my only concern here is there is no way we can enforce the phy 
reference is added in the platform_data structure.
That is what it is there for. That completely
> eliminates the need to housekeep a new set of data structures.

Ok. Makes sense.

Thanks
Kishon
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