From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Peter Senna Tschudin <peter.senna@collabora.com>
Cc: dri-devel@lists.freedesktop.org,
Peter Senna Tschudin <peter.senna@collabora.co.uk>,
Rob Herring <robh@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Daniel Vetter <daniel.vetter@ffwll.ch>,
Peter Senna Tschudin <peter.senna@gmail.com>,
Takashi Iwai <tiwai@suse.com>, Yakir Yang <ykk@rock-chips.com>,
Jiri Slaby <jslaby@suse.cz>,
Martyn Welch <martyn.welch@collabora.co.uk>,
Ian Campbell <ijc+devicetree@hellion.org.uk>,
Russell King <linux@armlinux.org.uk>,
Javier Martinez Canillas <javier@dowhile0.org>,
Thierry Reding <treding@nvidia.com>,
Guenter Roeck <linux@roeck-us.net>,
martin.donnelly@ge.com,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
Pawel Moll <pawel.moll@arm.com>,
Mauro Carvalho Chehab <mchehab@osg.samsung.com>,
enric.balletbo@collabora.com,
Russell King <rmk+kernel@armlinux.org.uk>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"linux-kernel@vger.kernel.org " <linux-kernel@vger.kernel.org>,
"kernel@pengutronix.de" <kernel@pengutronix.de>,
Kumar Gala <galak@codeaurora.org>,
Fabio Estevam <fabio.estevam@nxp.com>,
Andrew Morton <akpm@linux-foundation.org>,
Shawn Guo <shawnguo@kernel.org>,
David Miller <davem@davemloft.net>
Subject: Re: [PATCH V7 1/4] Documentation/devicetree/bindings: b850v3_lvds_dp
Date: Thu, 19 Jan 2017 13:49:25 +0200 [thread overview]
Message-ID: <6829547.Y11xI2zT5C@avalon> (raw)
In-Reply-To: <20170119092532.GB29457@collabora.com>
Hi Peter,
On Thursday 19 Jan 2017 10:25:32 Peter Senna Tschudin wrote:
> On Thu, Jan 19, 2017 at 10:17:45AM +0200, Laurent Pinchart wrote:
> > On Thursday 19 Jan 2017 09:12:14 Peter Senna Tschudin wrote:
> >> On Wed, Jan 18, 2017 at 11:10:58PM +0200, Laurent Pinchart wrote:
> >>> 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@kernel.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@collabora.co.uk>
> >>>>>>>>>> Cc: Martin Donnelly <martin.donnelly@ge.com>
> >>>>>>>>>> Cc: Javier Martinez Canillas <javier@dowhile0.org>
> >>>>>>>>>> Cc: Enric Balletbo i Serra <enric.balletbo@collabora.com>
> >>>>>>>>>> Cc: Philipp Zabel <p.zabel@pengutronix.de>
> >>>>>>>>>> Cc: Rob Herring <robh@kernel.org>
> >>>>>>>>>> Cc: Fabio Estevam <fabio.estevam@nxp.com>
> >>>>>>>>>> Signed-off-by: Peter Senna Tschudin <peter.senna@collabora.com>
> >>>>>>>>> ---
> >>>>>>>>>> There was an Acked-by from Rob Herring <robh@kernel.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 +++++++++
> >>>>>>>>>
> >>>>>>>>> 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 ?
> >>
> >> Each bridge has it's own external flash containing a binary firmware.
> >> The goal of the firmware is to configure the output end based on the
> >> input end. This is part of what makes handling EDID and HPD challenging.
> >>
> >>>> 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.
> >>
> >> Ah thanks. So for now the single DT node approach is acceptable, right?
> >> The problem is that even if the driver is getting better on each
> >> iteration, the single DT node for two chips issue comes back often and I
> >> believe is _the_ issue preventing the driver from getting upstream. V1
> >> was sent ~ 8 months ago...
> >>
> >> Can I have some blessing on the single DT node approach for now?
> >
> > With the "DT as an ABI" approach, I'm afraid not. Temporary hacks are
> > acceptable on the driver side, but you need two nodes in DT.
>
> So can I make two node DT "in the right way" and work around current
> connectors vs. bridge limitations on the driver side? This seems to be
> doable.
>
> Then I could fix bridge API, with my own driver and update API clients
> affected by the change...
I'm willing to discuss that as long as the DT bindings are correct, yes.
> >> I'm one of the 3 proposed maintainers for the driver, and I'm willing to
> >> maintain the driver on the long run, as is the same with the other two
> >> proposed maintainers. So when the time to split the node in two comes,
> >> we will be around, and willing to do it ourselves.
> >
> > How about putting that team of 3 maintainers to work on fixing the problem
> > in the bridge API ? :-)
>
> Guess you would be a good lawyer! My point was not exactly that we could
> work in parallel. Point was that there is redundancy in case one or two
> of us loose interest. But nice try! :-)
>
> Chances of having resources to fix bridge API and clients were better 6
> months ago, but let me see what I can get. Last blocking issue was the
> migration to atomic, now this. I'm going to need to answer what the next
> blocking issue is going to be.
>
> Actually in these ~8 months one bit of the required changes was
> accepted: dc80d7038883, but this was generic and not related to our
> specific use case.
--
Regards,
Laurent Pinchart
next prev parent reply other threads:[~2017-01-19 12:13 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-01 20:24 [PATCH V7 0/4] Add driver for GE B850v3 LVDS/DP++ Bridge Peter Senna Tschudin
2017-01-01 20:24 ` [PATCH V7 1/4] Documentation/devicetree/bindings: b850v3_lvds_dp Peter Senna Tschudin
2017-01-03 22:51 ` Rob Herring
2017-01-03 23:34 ` Peter Senna Tschudin
2017-01-04 20:39 ` Rob Herring
2017-01-07 1:29 ` Peter Senna Tschudin
2017-01-10 21:04 ` Laurent Pinchart
2017-01-16 8:37 ` Peter Senna Tschudin
2017-01-18 21:10 ` Laurent Pinchart
2017-01-19 8:12 ` Peter Senna Tschudin
2017-01-19 8:17 ` Laurent Pinchart
2017-01-19 9:25 ` Peter Senna Tschudin
2017-01-19 11:49 ` Laurent Pinchart [this message]
2017-01-10 21:06 ` Laurent Pinchart
2017-01-01 20:24 ` [PATCH V7 2/4] MAINTAINERS: Add entry for GE B850v3 LVDS/DP++ Bridge Peter Senna Tschudin
2017-01-01 20:24 ` [PATCH V7 3/4] drm/bridge: Add driver " Peter Senna Tschudin
2017-01-02 11:26 ` Peter Senna Tschudin
2017-01-05 7:48 ` Archit Taneja
2017-01-28 14:16 ` Peter Senna Tschudin
2017-01-30 17:05 ` Jani Nikula
2017-02-01 9:44 ` Archit Taneja
2017-02-01 10:58 ` Peter Senna Tschudin
2017-02-01 11:35 ` Daniel Vetter
2017-02-01 12:21 ` Peter Senna Tschudin
2017-02-02 9:56 ` Archit Taneja
2017-02-02 1:46 ` Emil Velikov
2017-02-02 11:53 ` Peter Senna Tschudin
2017-02-02 12:37 ` Emil Velikov
2017-02-03 8:00 ` Daniel Vetter
2017-02-03 12:25 ` Emil Velikov
2017-02-06 8:45 ` Daniel Vetter
2017-01-01 20:24 ` [PATCH V7 4/4] dts/imx6q-b850v3: Use " Peter Senna Tschudin
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