Date: Fri, 13 Feb 2015 10:01:23 -0600
From: Felipe Balbi <balbi@ti.com>
To: Heikki Krogerus <heikki.krogerus@linux.intel.com>
CC: David Cohen <david.a.cohen@linux.intel.com>, Felipe Balbi <balbi@ti.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Baolu Lu <baolu.lu@linux.intel.com>, <linux-usb@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, Kishon Vijay Abraham I <kishon@ti.com>
Subject: Re: [PATCH 8/8] phy: add driver for TI TUSB1210 ULPI PHY
Message-ID: <20150213160123.GC22238@saruman.tx.rr.com>
Reply-To: <balbi@ti.com>
References: <1422025978-178336-1-git-send-email-heikki.krogerus@linux.intel.com>
 <1422025978-178336-9-git-send-email-heikki.krogerus@linux.intel.com>
 <20150213015242.GD21337@psi-dev26.jf.intel.com>
 <20150213123516.GB27695@kuha.fi.intel.com>
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On Fri, Feb 13, 2015 at 02:35:16PM +0200, Heikki Krogerus wrote:
> Hi,
>=20
> On Thu, Feb 12, 2015 at 05:52:42PM -0800, David Cohen wrote:
> > Hi Heikki,
> >=20
> > Sorry I am starting a new branch on this thread.
> > I need to go back to another topic on this same patch.
> >=20
> > 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.
> > >=20
> > > Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
> > > Cc: Kishon Vijay Abraham I <kishon@ti.com>
> > > ---
> >=20
> > [snip]
> >=20
> > > +	/* Store initial eye diagram optimisation value */
> > > +	ret =3D ulpi_read(ulpi, TUSB1210_VENDOR_SPECIFIC2);
> >=20
> > 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.
>=20
> 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.
>=20
> 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.
>=20
> 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.
>=20
> Maybe we should actually get them from three separate properties:
>=20
>         device_property_read_u8(dev, "datapolarity", &val);
>         ...
>         device_property_read_u8(dev, "zhsdrv", &val);
>         ...
>         device_property_read_u8(dev, "ihstx", &val);
>         ...
>=20
> What do you think?

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

--=20
balbi

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