linux-kernel - Re: [PATCHv3 07/14] HSI: Add common DT binding for HSI client devices

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Message-ID: <20140425183225.GC22721@earth.universe>
Date:	Fri, 25 Apr 2014 20:32:26 +0200
From:	Sebastian Reichel <sre@...nel.org>
To:	Rob Herring <robherring2@...il.com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Shubhrajyoti Datta <omaplinuxkernel@...il.com>,
	Carlos Chinea <cch.devel@...il.com>,
	Tony Lindgren <tony@...mide.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Kumar Gala <galak@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-omap <linux-omap@...r.kernel.org>,
	Pali Rohár <pali.rohar@...il.com>,
	Ивайло Димитров 
	<freemangordon@....bg>,
	Joni Lapilainen <joni.lapilainen@...il.com>,
	Aaro Koskinen <aaro.koskinen@....fi>
Subject: Re: [PATCHv3 07/14] HSI: Add common DT binding for HSI client devices

On Mon, Apr 21, 2014 at 11:52:11AM -0500, Rob Herring wrote:
> On Fri, Mar 28, 2014 at 7:31 PM, Sebastian Reichel <sre@...nel.org> wrote:
> > Implement and document generic DT bindings for HSI clients.
> >
> > Signed-off-by: Sebastian Reichel <sre@...nel.org>
> 
> Seems pretty reasonable although I know little about HSI.

ok.

> > ---
> >  .../devicetree/bindings/hsi/client-devices.txt     |  44 +++++
> >  drivers/hsi/hsi.c                                  | 197 ++++++++++++++++++++-
> >  include/linux/hsi/hsi.h                            |   2 +
> >  3 files changed, 241 insertions(+), 2 deletions(-)
> >  create mode 100644 Documentation/devicetree/bindings/hsi/client-devices.txt
> >
> > diff --git a/Documentation/devicetree/bindings/hsi/client-devices.txt b/Documentation/devicetree/bindings/hsi/client-devices.txt
> > new file mode 100644
> > index 0000000..7504cb1
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/hsi/client-devices.txt
> > @@ -0,0 +1,44 @@
> > +Each HSI port is supposed to have one child node, which
> > +symbols the remote device connected to the HSI port. The
> > +following properties are standardized for HSI clients:
> > +
> > +Required HSI configuration properties:
> > +
> > +- reg:                 A list of channel ids
> > +
> > +- hsi-rx-mode:         Receiver Bit transmission mode ("stream" or "frame")
> > +- hsi-tx-mode:         Transmitter Bit transmission mode ("stream" or "frame")
> > +- hsi-mode:            May be used instead hsi-rx-mode and hsi-tx-mode if
> > +                       the transmission mode is the same for receiver and
> > +                       transmitter
> > +- hsi-speed-kbps:      Max bit transmission speed in kbit/s
> > +- hsi-flow:            RX flow type ("synchronized" or "pipeline")
> > +- hsi-arb-mode:                Arbitration mode for TX frame ("round-robin", "priority")
> > +
> > +Optional HSI configuration properties:
> > +
> > +- reg-names:           A list with one name per channel specified in the
> > +                       reg property
> > +
> > +
> > +Device Tree node example for an HSI client:
> > +
> > +hsi-controller {
> > +       hsi-port {
> > +               modem: hsi-client {
> > +                       compatible = "nokia,n900-modem";
> 
> Is there only 1 version of HSI? If not, then perhaps you need to
> know what version a client is.

There is HSI (High-speed Synchronous Serial Interface) and a legacy
variant from Texas Instruments called SSI (Synchronous Serial Interface).
The main difference is the speed and I don't think the difference
must be encoded in the Device Tree.

> > +                       reg = <0>, <1>, <2>, <3>;
> 
> Where do these numbers get defined?

HSI provides multiple serial connections and this describes which
channels are used for the remote device.

>Are they always 0-N?

From what I understand they don't have to.

> I don't see much advantage to using reg. Perhaps something like
> hsi-channel-ids would be better.

I will change it to hsi-channel-ids for PATCHv4.

-- Sebastian

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