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Subject: Re: [PATCH v5 3/7] dt-bindings: display: Add ingenic,jz4780-dw-hdmi
 DT Schema
From:   "H. Nikolaus Schaller" <hns@goldelico.com>
In-Reply-To: <8XUI0R.KDQ64KIMI9BU@crapouillou.net>
Date:   Sun, 7 Nov 2021 14:43:33 +0100
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>,
        Daniel Vetter <daniel@ffwll.ch>,
        Neil Armstrong <narmstrong@baylibre.com>,
        Robert Foss <robert.foss@linaro.org>,
        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 list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
        linux-mips <linux-mips@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Discussions about the Letux Kernel 
        <letux-kernel@openphoenux.org>, Jonas Karlman <jonas@kwiboo.se>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Rob Herring <robh@kernel.org>
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References: <cover.1633436959.git.hns@goldelico.com>
 <518d5db83e84e3f0326854c5afb53a92e7ae4e41.1633436959.git.hns@goldelico.com>
 <8XUI0R.KDQ64KIMI9BU@crapouillou.net>
To:     Paul Cercueil <paul@crapouillou.net>
Precedence: bulk

Hi,

> Am 05.10.2021 um 22:43 schrieb Paul Cercueil <paul@crapouillou.net>:
>=20
> Hi Nikolaus,
>=20
> Le mar., oct. 5 2021 at 14:29:15 +0200, H. Nikolaus Schaller =
<hns@goldelico.com> a =C3=A9crit :
>> 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.
>=20
> My dmesg disagrees:
> dw-hdmi-ingenic 10180000.hdmi: Detected HDMI TX controller v1.31a with =
HDCP (DWC HDMI 3D TX PHY)

mine as well.

>=20
> 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.

>=20
>> +
>> +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
>=20
> 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