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

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Message-ID: <2088084.GDlN6tZSQv@avalon>
Date:   Wed, 18 Jan 2017 23:10:58 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Peter Senna Tschudin <peter.senna@...labora.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

Hi Peter,

On Monday 16 Jan 2017 09:37:11 Peter Senna Tschudin wrote:
> On Tue, Jan 10, 2017 at 11:04:58PM +0200, Laurent Pinchart wrote:
> > 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.

Which firmware are you talking about ? Firmware running on the bridges, or 
somewhere else ?

> 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?

You didn't, we did :-) I've been telling for quite some time now that we must 
decouple bridges from connectors, and this is another example of why we have 
such a need. Bridges should expose additional functions needed to implement 
connector operations, and the connector should be instantiated by the display 
driver with the help of bridge operations. You could then create a connector 
that relies on one bridge to read the EDID and on the other bridge to handle 
HPD.

-- 
Regards,

Laurent Pinchart