linux-kernel - Re: [PATCH 1/3] Documentation: dt: dwc3: Add snps,configure-fladj property

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Date:	Thu, 23 Jul 2015 11:57:29 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Badola Nikhil <nikhil.badola@...escale.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"balbi@...com" <balbi@...com>
Subject: Re: [PATCH 1/3] Documentation: dt: dwc3: Add snps,configure-fladj
 property

On Thu, Jul 23, 2015 at 11:52:19AM +0100, Badola Nikhil wrote:
> > -----Original Message-----
> > From: Mark Rutland [mailto:mark.rutland@....com]
> > Sent: Thursday, July 23, 2015 3:27 PM
> > To: Badola Nikhil-B46172
> > Cc: linux-kernel@...r.kernel.org; devicetree@...r.kernel.org; balbi@...com
> > Subject: Re: [PATCH 1/3] Documentation: dt: dwc3: Add snps,configure-fladj
> > property
> > 
> > On Thu, Jul 23, 2015 at 11:09:21AM +0100, Nikhil Badola wrote:
> > > Add property snps,configure-fladj for enabling post silicon frame
> > > length adjustment
> > >
> > > Signed-off-by: Nikhil Badola <nikhil.badola@...escale.com>
> > > ---
> > >  Documentation/devicetree/bindings/usb/dwc3.txt | 1 +
> > >  1 file changed, 1 insertion(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/usb/dwc3.txt
> > > b/Documentation/devicetree/bindings/usb/dwc3.txt
> > > index 0815eac..90c3972 100644
> > > --- a/Documentation/devicetree/bindings/usb/dwc3.txt
> > > +++ b/Documentation/devicetree/bindings/usb/dwc3.txt
> > > @@ -40,6 +40,7 @@ Optional properties:
> > >   - snps,hird-threshold: HIRD threshold
> > >   - snps,hsphy_interface: High-Speed PHY interface selection between
> > "utmi" for
> > >     UTMI+ and "ulpi" for ULPI when the DWC_USB3_HSPHY_INTERFACE has
> > value 3.
> > > + - snps,configure-fladj: enables post-silicon frame length adjustment
> > 
> > Could you elaborate on what this means and why you think it's necessary?
> 
> This property enables the use of GFLADJ_30MHZ field value of gfladj register for frame length 
> adjustment instead of considering from the sideband input signal fladj_30mhz_reg from SOC. 
> This is required when signal fladj_30mhz_reg is connected to a wrong value or is not valid as 
> in our case, hence post-silicon.

Ok, so this is basically an override for the GFLADJ_30MHZ field of the
gfladj register when there was a problem at integration time.

> However this field can be used to adjust any offset ranging from 00h to 3Fh, from the
> clock source generating SOF(start of frame) packets. Thus, this property can be added to device 
> tree with appropriate adjustment value.

It takes a value? The description above makes it sound like a boolean
property.

I'd expect a description more like:

- snps,fladj-override: Value for GFLADJ_30MHZ when the fladj_30mhz_reg
  signal is invalid or incorrect.

Which makes it clear what the value is and when it should be set.

Thanks,
Mark.
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