linux-kernel - Re: [PATCH v3 17/25] dt-bindings: panel: Add Bananapi S070WV20-CT16 ICN6211 MIPI-DSI to RGB bridge

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Message-ID: <CAMty3ZAWkX8YSRzFs_GS2O4+=pf68e4EuSMym+_XpCe3_4-2yw@mail.gmail.com>
Date:   Tue, 6 Nov 2018 23:38:53 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     a.hajda@...sung.com
Cc:     Chen-Yu Tsai <wens@...e.org>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Icenowy Zheng <icenowy@...c.io>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Vasily Khoruzhick <anarsoul@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        David Airlie <airlied@...ux.ie>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Michael Trimarchi <michael@...rulasolutions.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi@...glegroups.com
Subject: Re: [PATCH v3 17/25] dt-bindings: panel: Add Bananapi S070WV20-CT16
 ICN6211 MIPI-DSI to RGB bridge

On Wed, Oct 31, 2018 at 2:45 PM Andrzej Hajda <a.hajda@...sung.com> wrote:
>
> On 31.10.2018 09:58, Chen-Yu Tsai wrote:
> > On Wed, Oct 31, 2018 at 4:53 PM Andrzej Hajda <a.hajda@...sung.com> wrote:
> >> On 26.10.2018 16:43, Jagan Teki wrote:
> >>> Bananapi S070WV20-CT16 ICN6211 is 800x480, 4-lane MIPI-DSI to RGB
> >>> bridge panel, which is available on same PCB with 24-bit RGB interface.
> >>>
> >>> So, this patch adds DSI specific binding details on existing
> >>> dt-bindings file.
> >>>
> >>> Signed-off-by: Jagan Teki <jagan@...rulasolutions.com>
> >>> ---
> >>> Changes for v3:
> >>> - Use existing binding doc and update dsi details
> >>> Changes for v2:
> >>> - none
> >>>
> >>>  .../display/panel/bananapi,s070wv20-ct16.txt  | 31 +++++++++++++++++--
> >>>  1 file changed, 29 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/display/panel/bananapi,s070wv20-ct16.txt b/Documentation/devicetree/bindings/display/panel/bananapi,s070wv20-ct16.txt
> >>> index 35bc0c839f49..b7855dc7c66f 100644
> >>> --- a/Documentation/devicetree/bindings/display/panel/bananapi,s070wv20-ct16.txt
> >>> +++ b/Documentation/devicetree/bindings/display/panel/bananapi,s070wv20-ct16.txt
> >>> @@ -1,12 +1,39 @@
> >>>  Banana Pi 7" (S070WV20-CT16) TFT LCD Panel
> >>>
> >>> +S070WV20-CT16 is 7" 800x480 panel connected through a 24-bit RGB interface.
> >>> +
> >>> +Depending on the variant, the PCB attached to the panel module either
> >>> +supports DSI, or DSI + 24-bit RGB. DSI is converted to 24-bit RGB via
> >>> +an onboard ICN6211 MIPI DSI - RGB bridge chip, then fed to the panel
> >>> +itself
> >> As I understand this is display board, which contains 'pure' RGB panel
> >> S070WV20-CT16 and optionally ICN6211 DSI->RGB bridge.
> >> These are separate devices, just connected by vendor to simplify its
> >> assembly. Why don't you create then bridge driver for ICN6211 and RGB
> >> panel driver for S070WV20-CT16 - it looks more generic.
> >> Then you can describe both in dts and voila.
> >> Creating drivers for every combo of devices (panel + bridge), just
> >> because some vendor sells them together seems incorrect - we have
> >> devicetree for it.
> > Rob suggested this, and also the opposite: using the same
> > "bananapi,s070wv20-ct16"
> > compatible string for both types of connections, and have the driver deal with
> > detecting the bus type.
> >
> > The thing about the bridge chip is that there's no available datasheet that
> > describes all the parts of the init sequence, in fact none at all. I managed
> > to work out some bits, but the others remain a mystery and must be hard-coded
> > to match the panel. That would work against having a generic bridge driver.
>
>
> But it is common for many chips - 1st version of the driver is developed
> on one platform and it supports only one configuration, if next platform
> with the same cheap appears the driver is augmented if necessary.

At-least few of the commands from panel initialization code, the
respective opcode data values are based on panel timings and even
clock value is different in DSI. I think it look hard to try bridge
driver for these restrictions, do you have any suggestions?