linux-kernel - Re: [PATCH 8/8] phy: add driver for TI TUSB1210 ULPI PHY

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Message-ID: <20150213160123.GC22238@saruman.tx.rr.com>
Date:	Fri, 13 Feb 2015 10:01:23 -0600
From:	Felipe Balbi <balbi@...com>
To:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
CC:	David Cohen <david.a.cohen@...ux.intel.com>,
	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Baolu Lu <baolu.lu@...ux.intel.com>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Kishon Vijay Abraham I <kishon@...com>
Subject: Re: [PATCH 8/8] phy: add driver for TI TUSB1210 ULPI PHY

On Fri, Feb 13, 2015 at 02:35:16PM +0200, Heikki Krogerus wrote:
> Hi,
> 
> On Thu, Feb 12, 2015 at 05:52:42PM -0800, David Cohen wrote:
> > Hi Heikki,
> > 
> > Sorry I am starting a new branch on this thread.
> > I need to go back to another topic on this same patch.
> > 
> > On Fri, Jan 23, 2015 at 05:12:58PM +0200, Heikki Krogerus wrote:
> > > TUSB1210 ULPI PHY has vendor specific register for eye
> > > diagram tuning. On some platforms the system firmware has
> > > set optimized value to it. In order to not loose the
> > > optimized value, the driver stores it during probe and
> > > restores it every time the PHY is powered back on.
> > > 
> > > Signed-off-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> > > Cc: Kishon Vijay Abraham I <kishon@...com>
> > > ---
> > 
> > [snip]
> > 
> > > +	/* Store initial eye diagram optimisation value */
> > > +	ret = ulpi_read(ulpi, TUSB1210_VENDOR_SPECIFIC2);
> > 
> > We can't rely on eye diagram optimization value here. It's possible the
> > phy went through reset (e.g. module unloading/loading).
> > We need a more consistent method. Could we use _DSD instead? That would
> > be more compatible with DT too.
> 
> I'm don't have any problem with getting the value from a property.
> Sounds like the correct thing to do. Are you thinking about putting
> that _DSD method to the ACPI device object for the dwc3? The correct
> place would probable be separate device object for the PHY, but if we
> do that we need to consider how that object is bound to the ulpi
> device. There are few ways we can do that, so it requires some
> thinking.
> 
> In any case this driver we can already implement so that it expects to
> get the value from property. We just need the name for it.
> 
> The register has actually separate fields for High speed output
> impedance configuration and High speed output driver strength
> configuration for eye diagram tuning, plus control bit for DP/DM swap.
> 
> Maybe we should actually get them from three separate properties:
> 
>         device_property_read_u8(dev, "datapolarity", &val);
>         ...
>         device_property_read_u8(dev, "zhsdrv", &val);
>         ...
>         device_property_read_u8(dev, "ihstx", &val);
>         ...
> 
> What do you think?

it's probably better to pass each value and let the driver calculate the
register contents like this.

-- 
balbi

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