Re: [PATCH v4 10/15] usb: phy: msm: Add device tree support and binding information

From: "Ivan T. Ivanov" <iivanov@mm-sol.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: "balbi@ti.com" <balbi@ti.com>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	"rob.herring@calxeda.com" <rob.herring@calxeda.com>,
	Pawel Moll <Pawel.Moll@arm.com>,
	"swarren@wwwdotorg.org" <swarren@wwwdotorg.org>,
	"ijc+devicetree@hellion.org.uk" <ijc+devicetree@hellion.org.uk>,
	"davidb@codeaurora.org" <davidb@codeaurora.org>,
	"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
	"linux-arm-msm@vger.kernel.org" <linux-arm-msm@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>
Subject: Re: [PATCH v4 10/15] usb: phy: msm: Add device tree support and binding information
Date: Wed, 11 Dec 2013 11:45:36 +0200	[thread overview]
Message-ID: <1386755136.16289.26.camel@iivanov-dev.int.mm-sol.com> (raw)
In-Reply-To: <20131205104150.GJ29200@e106331-lin.cambridge.arm.com>

Hi, 

On Thu, 2013-12-05 at 10:41 +0000, Mark Rutland wrote: 
> On Mon, Nov 18, 2013 at 12:54:37PM +0000, Ivan T. Ivanov wrote:
> > Hi Mark, 
> > 
> > On Fri, 2013-11-15 at 16:38 +0000, Mark Rutland wrote: 
> > > On Tue, Nov 12, 2013 at 02:51:45PM +0000, Ivan T. Ivanov wrote:
> > > > From: "Ivan T. Ivanov" <iivanov@mm-sol.com>
> > > > 
> > > > Allows MSM OTG controller to be specified via device tree.
> > > > 
> > > > Signed-off-by: Ivan T. Ivanov <iivanov@mm-sol.com>
> > > > Cc: devicetree@vger.kernel.org
> > > > ---
> > > >  .../devicetree/bindings/usb/msm-hsusb.txt          |   57 +++++++++++++-
> > > >  drivers/usb/phy/phy-msm-usb.c                      |   79 +++++++++++++++++---
> > > >  2 files changed, 124 insertions(+), 12 deletions(-)
> 
> [...]
> 
> > > > +
> > > > +- dr_mode:		One of "host", "peripheral" or "otg". Defaults to "otg"
> > > 
> > > If this has a default and thus isn't required, it should be listed as
> > > optional.
> > 
> > This is part of the standard USB bindings, Perhaps I could just
> > refer to:  Documentation/devicetree/bindings/usb/generic.txt
> 
> That would be fine, but it should also be moved to the optional
> properties section.

Ok.

> 
> > 
> > 
> > > 
> > > > +
> > > > +- vdccx-supply:	phandle to the regulator for the vdd supply for
> > > > +				digital circuit operation.
> > > > +- v1p8-supply:	phandle to the regulator for the 1.8V supply
> > > > +- v3p3-supply:	phandle to the regulator for the 3.3V supply
> > > > +
> > > > +- qcom,otg-control: OTG control (VBUS and ID notifications) can be one of
> > > > +				1 - PHY control
> > > > +				2 - PMIC control
> > > > +				3 - User control (via debugfs)
> > > 
> > > NAK. This does not seem like a description of the hardware, and given
> > > the debugfs comment is fundamentally tied to the way Linux functions
> > > today.
> > 
> > I will remove option 3, but rest are really property of the chipset. 
> 
> Can you elaborate on the diffence please?

Difference is how VBUS, ID changes, Accessory and Charger
detection is handled. In older chips-sets they are handled
by PHY controller, while now they are handled by external
PMIC logic.

> 
> > 
> > > 
> > > > +
> > > > +Optional properties:
> > > > +- qcom,phy-init-sequence: PHY configuration sequence. val, reg pairs
> > > > +				terminate with -1
> > > 
> > > What is this? I'm really not keen on having arbitrary register/memory
> > > poking sequences in the dt.
> > 
> > This is related Device Mode Eye Diagram test and values used could be
> > different between chipsets.
> 
> Ok. Then we should encode the tuning data rather than adding a mechanism
> to allow for writes to arbitrary addresses.

Currently: 

for msm8226 sequence is < 0x44 0x80 0x68 0x81 0x24 0x82 0x13 0x83 >
for msm8974 sequence is < 0x63 0x81 >

I could reserve -1 as "do not program" value and document that 
values in this array will be written to ULPI interface with
ULPI_EXT_VENDOR_SPECIFIC as base address.

for msm8974 sequence will be < -1 0x63 >

> 
> > 
> > > 
> > > Why does it need to be terminated? Surely the size of the property tells
> > > you that it's terminated.
> > 
> > Yes. -1 termination could be done in driver.
> 
> Please do. There's no need for it to be in the DT.

Thanks. Ivan

> 
> Cheers,
> Mark.
> --
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