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Date:   Sun, 07 Nov 2021 19:03:03 +0000
From:   Paul Cercueil <paul@crapouillou.net>
Subject: Re: [PATCH v5 3/7] dt-bindings: display: Add ingenic,jz4780-dw-hdmi
 DT Schema
To:     "H. Nikolaus Schaller" <hns@goldelico.com>
Cc:     Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Kees Cook <keescook@chromium.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        David Airlie <airlied@linux.ie>,
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        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        Ezequiel Garcia <ezequiel@collabora.com>,
        Harry Wentland <harry.wentland@amd.com>,
        Sam Ravnborg <sam@ravnborg.org>,
        Maxime Ripard <maxime@cerno.tech>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Liam Girdwood <lgirdwood@gmail.com>,
        Mark Brown <broonie@kernel.org>,
        Paul Boddie <paul@boddie.org.uk>,
        OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS 
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Hi Nikolaus,

Le dim., nov. 7 2021 at 14:43:33 +0100, H. Nikolaus Schaller 
<hns@goldelico.com> a ?crit :
> Hi,
> 
>>  Am 05.10.2021 um 22:43 schrieb Paul Cercueil <paul@crapouillou.net>:
>> 
>>  Hi Nikolaus,
>> 
>>  Le mar., oct. 5 2021 at 14:29:15 +0200, H. Nikolaus Schaller 
>> <hns@goldelico.com> a ?crit :
>>>  From: Sam Ravnborg <sam@ravnborg.org>
>>>  Add DT bindings for the hdmi driver for the Ingenic JZ4780 SoC.
>>>  Based on .txt binding from Zubair Lutfullah Kakakhel
>>>  Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
>>>  Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
>>>  Cc: Rob Herring <robh@kernel.org>
>>>  Cc: devicetree@vger.kernel.org
>>>  ---
>>>  .../bindings/display/ingenic-jz4780-hdmi.yaml | 79 
>>> +++++++++++++++++++
>>>  1 file changed, 79 insertions(+)
>>>  create mode 100644 
>>> Documentation/devicetree/bindings/display/ingenic-jz4780-hdmi.yaml
>>>  diff --git 
>>> a/Documentation/devicetree/bindings/display/ingenic-jz4780-hdmi.yaml 
>>> b/Documentation/devicetree/bindings/display/ingenic-jz4780-hdmi.yaml
>>>  new file mode 100644
>>>  index 000000000000..5bcb342da86f
>>>  --- /dev/null
>>>  +++ 
>>> b/Documentation/devicetree/bindings/display/ingenic-jz4780-hdmi.yaml
>>>  @@ -0,0 +1,79 @@
>>>  +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
>>>  +%YAML 1.2
>>>  +---
>>>  +$id: 
>>> http://devicetree.org/schemas/display/ingenic-jz4780-hdmi.yaml#
>>>  +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>>  +
>>>  +title: Bindings for Ingenic JZ4780 HDMI Transmitter
>>>  +
>>>  +maintainers:
>>>  +  - H. Nikolaus Schaller <hns@goldelico.com>
>>>  +
>>>  +description: |
>>>  +  The HDMI Transmitter in the Ingenic JZ4780 is a Synopsys 
>>> DesignWare HDMI 1.4
>>>  +  TX controller IP with accompanying PHY IP.
>> 
>>  My dmesg disagrees:
>>  dw-hdmi-ingenic 10180000.hdmi: Detected HDMI TX controller v1.31a 
>> with HDCP (DWC HDMI 3D TX PHY)
> 
> mine as well.
> 
>> 
>>  Or am I comparing apples to oranges?
> 
> There is a document called "JZ4780 High Efficiency Engine for Mobile 
> Device"
> (JZ4780_PB.pdf) which says
> 
> "24-bit parallel/serial TFT interface, HDMI 1.4a interface, LVDS 
> interface"
> 
> And the data sheet ("JZ4780 Mobile Application Processor Data Sheet 
> ") says: "Support HDMI 1.4a Interface"
> 
> Finally, the programming manual also says "Support HDMI 1.4a 
> Interface".
> 
> So what is correct?
> 
> dmesg may return something else. E.g. silicon revision 1.31a
> while the interface is HDMI protocol revision 1.4a compatible?
> 
> Trying to find something about "hdmi 1.31a" did only lead to some
> "Synopsys' HAPS-51 eval platform" [1].
> 
> Looking at HDMI standards [2] I can only find HDMI 1.3 and 1.3a but 
> no HDMI 1.31a.
> 
> [1] 
> https://www.digital-cp.com/hdcp-products/haps51-hdmi-tx-platform-dwc-hdmi-tx-controller-131a-ea-hdmi-3d-tx-phy-tsmc40g-ip
> [2] https://en.wikipedia.org/wiki/HDMI#Version_1.3
> 
> Well it may also be some Synopsys-internal designation 1.31a 
> referring so something
> newer than HDMI 1.3a which became the HDMI 1.4 standard (released 
> June 2009)...
> 
> Whom should we believe? What the chip tells or what the data sheet 
> and programming
> manual says?
> 
> I tend to keep confusion low and stay with "HDMI 1.4" in the bindings 
> because
> there is no offical "HDMI 1.31a" standard. And HDMI 1.4 was already 
> some years old
> when the jz4780 was released. So it is likely that the chip 
> identification just
> returns 1.31a (maybe Ingenic licenced an interim release VHDL) 
> although the standard
> was later officially named 1.4a.

Fair enough. Let's keep "HDMI 1.4" until proven otherwise.

Cheers,
-Paul

>> 
>>>  +
>>>  +allOf:
>>>  +  - $ref: bridge/synopsys,dw-hdmi.yaml#
>>>  +
>>>  +properties:
>>>  +  compatible:
>>>  +    const: ingenic,jz4780-dw-hdmi
>>>  +
>>>  +  reg-io-width:
>>>  +    const: 4
>>>  +
>>>  +  clocks:
>>>  +    maxItems: 2
>>>  +
>>>  +  hdmi-5v-supply:
>>>  +    description: Optional regulator to provide +5V at the 
>>> connector
>>>  +
>>>  +  ddc-i2c-bus:
>>>  +    description: An I2C interface if the internal DDC I2C driver 
>>> is not to be used
>> 
>>  This property is used within 
>> (drivers/gpu/drm/bridge/synopsys/dw-hdmi.c); I think it would make 
>> sense to move it to bridge/synopsys,dw-hdmi.yaml.
> 
> It is indeed more general and not jz4780 specific. I'll move it for 
> v6.
> 
> BR and thanks,
> Nikolaus
>