linux-kernel - Re: [PATCH v2 01/14] usb: phy: nop: Add device tree support and binding information

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Message-ID: <20130211153112.GA15013@e106331-lin.cambridge.arm.com>
Date:	Mon, 11 Feb 2013 15:31:13 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Roger Quadros <rogerq@...com>
Cc:	"tony@...mide.com" <tony@...mide.com>,
	"b-cousson@...com" <b-cousson@...com>,
	"balbi@...com" <balbi@...com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"stern@...land.harvard.edu" <stern@...land.harvard.edu>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"kishon@...com" <kishon@...com>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 01/14] usb: phy: nop: Add device tree support and
 binding information

Hi Roger,

On Mon, Feb 11, 2013 at 03:14:26PM +0000, Roger Quadros wrote:
> On 02/11/2013 01:40 PM, Mark Rutland wrote:
> > Hello,
> > 
> > On Thu, Feb 07, 2013 at 04:02:41PM +0000, Roger Quadros wrote:
> >> The PHY clock, clock rate, VCC regulator and RESET regulator
> >> can now be provided via device tree.
> >>
> >> Signed-off-by: Roger Quadros <rogerq@...com>
> >> Acked-by: Felipe Balbi <balbi@...com>
> >> ---
> >>  .../devicetree/bindings/usb/usb-nop-xceiv.txt      |   34 ++++++++++++++++++
> >>  drivers/usb/otg/nop-usb-xceiv.c                    |   36 +++++++++++++++----
> >>  2 files changed, 62 insertions(+), 8 deletions(-)
> >>  create mode 100644 Documentation/devicetree/bindings/usb/usb-nop-xceiv.txt
> >>
> >> diff --git a/Documentation/devicetree/bindings/usb/usb-nop-xceiv.txt b/Documentation/devicetree/bindings/usb/usb-nop-xceiv.txt
> >> new file mode 100644
> >> index 0000000..d7e2726
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/usb/usb-nop-xceiv.txt
> >> @@ -0,0 +1,34 @@
> >> +USB NOP PHY
> >> +
> >> +Required properties:
> >> +- compatible: should be usb-nop-xceiv
> > 
> > This might be better as "linux,usb-no-xceiv", given this is a Linux-specific
> > 'device'.
> > 
> > Saying that, I'm not sure I understand why this device needs to be instantiated
> > from devicetree. As I understand it from looking at the driver, it's purely a
> > Linux implementation detail used in the case of autonomous PHYs, and not an
> > actual piece of hardware or firmware system. I must admit to being unfamiliar
> > with this area of hardware, have I misunderstood somethign here?
> 
> The PHY is a physical device and may need resources like power and clock to be functional.
> The only reason that driver is named NOP is that many USB controllers know how to talk to
> the standard PHYs and don't need any interface/management software.

Ok. That makes sense. Apologies for the noise.

> 
> The PHY driver you are looking at most likely doesn't have the recent changes I wrote to
> manage the PHY clock/reset/power. i.e. patches 3, 4 and 5 in the series
>  https://lkml.org/lkml/2013/1/28/275
> 
> Before this, the ehci-omap driver was trying to manage the PHY power and reset, which was
> wrong.

Yes. That makes a lot more sense now.

Thanks for the info!

Thanks,
Mark.

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