linux-kernel - Re: [PATCH V7 1/4] Documentation/devicetree/bindings: b850v3_lvds

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Message-ID: <20170116083711.GA18775@collabora.com>
Date:   Mon, 16 Jan 2017 09:37:11 +0100
From:   Peter Senna Tschudin <peter.senna@...labora.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     dri-devel@...ts.freedesktop.org,
        Peter Senna Tschudin <peter.senna@...labora.co.uk>,
        Rob Herring <robh@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Peter Senna Tschudin <peter.senna@...il.com>,
        Takashi Iwai <tiwai@...e.com>, Yakir Yang <ykk@...k-chips.com>,
        Jiri Slaby <jslaby@...e.cz>,
        Martyn Welch <martyn.welch@...labora.co.uk>,
        Ian Campbell <ijc+devicetree@...lion.org.uk>,
        Russell King <linux@...linux.org.uk>,
        Javier Martinez Canillas <javier@...hile0.org>,
        Thierry Reding <treding@...dia.com>,
        Guenter Roeck <linux@...ck-us.net>, martin.donnelly@...com,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Pawel Moll <pawel.moll@....com>,
        Mauro Carvalho Chehab <mchehab@....samsung.com>,
        enric.balletbo@...labora.com,
        Russell King <rmk+kernel@...linux.org.uk>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org " <linux-kernel@...r.kernel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        Kumar Gala <galak@...eaurora.org>,
        Fabio Estevam <fabio.estevam@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shawn Guo <shawnguo@...nel.org>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH V7 1/4] Documentation/devicetree/bindings: b850v3_lvds_dp

On Tue, Jan 10, 2017 at 11:04:58PM +0200, Laurent Pinchart wrote:
> Hi Peter,

Laurent!

> 
> On Saturday 07 Jan 2017 01:29:52 Peter Senna Tschudin wrote:
> > On 04 January, 2017 21:39 CET, Rob Herring wrote:
> > > On Tue, Jan 3, 2017 at 5:34 PM, Peter Senna Tschudin wrote:
> > >> On 03 January, 2017 23:51 CET, Rob Herring <robh@...nel.org> wrote:
> > >>> On Sun, Jan 01, 2017 at 09:24:29PM +0100, Peter Senna Tschudin wrote:
> > >>>> Devicetree bindings documentation for the GE B850v3 LVDS/DP++
> > >>>> display bridge.
> > >>>> 
> > >>>> Cc: Martyn Welch <martyn.welch@...labora.co.uk>
> > >>>> Cc: Martin Donnelly <martin.donnelly@...com>
> > >>>> Cc: Javier Martinez Canillas <javier@...hile0.org>
> > >>>> Cc: Enric Balletbo i Serra <enric.balletbo@...labora.com>
> > >>>> Cc: Philipp Zabel <p.zabel@...gutronix.de>
> > >>>> Cc: Rob Herring <robh@...nel.org>
> > >>>> Cc: Fabio Estevam <fabio.estevam@....com>
> > >>>> Signed-off-by: Peter Senna Tschudin <peter.senna@...labora.com>
> > >>>> ---
> > >>>> There was an Acked-by from Rob Herring <robh@...nel.org> for V6, but
> > >>>> I changed the bindings to use i2c_new_secondary_device() so I
> > >>>> removed it from the commit message.
> > >>>> 
> > >>>>  .../devicetree/bindings/ge/b850v3-lvds-dp.txt      | 39 ++++++++++++++
> > >>> Generally, bindings are not organized by vendor. Put in
> > >>> bindings/display/bridge/... instead.
> > >> 
> > >> Will change that.
> > >> 
> > >>>>  1 file changed, 39 insertions(+)
> > >>>>  create mode 100644
> > >>>>  Documentation/devicetree/bindings/ge/b850v3-lvds-dp.txt
> > >>>> 
> > >>>> diff --git a/Documentation/devicetree/bindings/ge/b850v3-lvds-dp.txt
> > >>>> b/Documentation/devicetree/bindings/ge/b850v3-lvds-dp.txt new file
> > >>>> mode 100644
> > >>>> index 0000000..1bc6ebf
> > >>>> --- /dev/null
> > >>>> +++ b/Documentation/devicetree/bindings/ge/b850v3-lvds-dp.txt
> > >>>> @@ -0,0 +1,39 @@
> > >>>> +Driver for GE B850v3 LVDS/DP++ display bridge
> > >>>> +
> > >>>> +Required properties:
> > >>>> +  - compatible : should be "ge,b850v3-lvds-dp".
> > >>> 
> > >>> Isn't '-lvds-dp' redundant? The part# should be enough.
> > >> 
> > >> b850v3 is the name of the product, this is why the proposed name. What
> > >> about, b850v3-dp2 dp2 indicating the second DP output?
> > >
> > > Humm, b850v3 is the board name? This node should be the name of the bridge
> > > chip.
> >
> > From the cover letter:
> > 
> > -- // --
> > There are two physical bridges on the video signal pipeline: a STDP4028(LVDS
> > to DP) and a STDP2690(DP to DP++).  The hardware and firmware made it
> > complicated for this binding to comprise two device tree nodes, as the
> > design goal is to configure both bridges based on the LVDS signal, which
> > leave the driver powerless to control the video processing pipeline. The
> > two bridges behaves as a single bridge, and the driver is only needed for
> > telling the host about EDID / HPD, and for giving the host powers to ack
> > interrupts. The video signal pipeline is as follows:
> > 
> >   Host -> LVDS|--(STDP4028)--|DP -> DP|--(STDP2690)--|DP++ -> Video output
> > -- // --
> 
> You forgot to prefix your patch series with [HACK] ;-)
> 
> How about fixing the issues that make the two DT nodes solution difficult ? 
> What are they ?

The Firmware and the hardware design. Both bridges, with stock firmware,
are fully capable of providig EDID information and handling interrupts.
But on this specific design, with this specific firmware, I need to read
EDID from one bridge, and handle interrupts on the other. Back when I
was starting the development I could not come up with a proper way to
split EDID and interrupts between two bridges in a way that would result
in a fully functional connector. Did I miss something?


> 
> -- 
> Regards,
> 
> Laurent Pinchart
>