linux-kernel - Re: [PATCH V2] USB: initialize or shutdown PHY when add or remove host controller

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Date:	Thu, 20 Jun 2013 15:17:49 +0300
From:	Felipe Balbi <balbi@...com>
To:	Chao Xie <xiechao.mail@...il.com>
CC:	Roger Quadros <rogerq@...com>, Chao Xie <chao.xie@...vell.com>,
	Alan Stern <stern@...land.harvard.edu>,
	"balbi@...com" <balbi@...com>,
	Greg KH <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH V2] USB: initialize or shutdown PHY when add or remove
 host controller

Hi,

On Thu, Jun 20, 2013 at 08:53:05AM +0800, Chao Xie wrote:
> >> @@ -2674,6 +2693,9 @@ void usb_remove_hcd(struct usb_hcd *hcd)
> >>                       free_irq(hcd->irq, hcd);
> >>       }
> >>
> >> +     if (hcd->phy)
> >> +             usb_phy_shutdown(hcd->phy);
> >> +
> >>       usb_put_dev(hcd->self.root_hub);
> >>       usb_deregister_bus(&hcd->self);
> >>       hcd_buffer_destroy(hcd);
> >>
> >
> > I still think that we shouldn't do this because it adds more confusion and is not
> > still a generic enough solution.
> >
> > 1) It is better for the piece of code that does usb_phy_get() to do usb_phy_init/shutdown,
> > else there will be lot of confusion. (Felipe pointed this out earlier).
> >
> > 2) There is no standard way of getting phy for different controllers. It is mostly platform
> > dependent and it is best to leave this to the controller drivers. (Pointed out by Alan).
> >
> > 3) Controllers can have multiple PHYs. e.g. ehci-omap has one PHY per port and it supports
> > 3 ports. This is also platform specific and difficult to handle generically.
> >
> > 4) Controllers can have specific timing requirements as to when the PHY is initialized relative
> > to the controller being initialized. I've pointed OMAP specific stuff in the earlier patch.
> >
> > Considering all these points, I think we should leave things as they are. It isn't that hard
> > for controllers to manage phy_init() and phy_shutdown(), and there is not much code space saved
> > when compared to the complexity it creates if we move them to HCD layer.
> >
> In fact, the PHY setting and handling is related to platform or SOC,
> and for different SOC they can
> have same EHCI HCD but they PHY handling can be different.
> Omap'a case is the example, and i think some other vendors may have
> silimar cases.
> From above point, It is better to leave the PHY initialization and
> shutdown to be done by each echi-xxx driver.
> 
> So Alan and Felipe
> What are your ideas about it?

If we have so many exceptions, then sure. But eventually, the common
case should be added generically with a flag so that non-generic cases
(like OMAP) can request to handle the PHY by themselves.

Alan ?

-- 
balbi

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