linux-kernel - Re: [PATCH 2/4] dt-bindings: display: panel: Add Himax HX83112B

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Message-ID: <cf3a0429-0c36-426f-b9b0-ae7749877bf3@kernel.org>
Date: Mon, 24 Feb 2025 09:16:25 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Luca Weiss <luca@...aweiss.eu>
Cc: ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org,
 Neil Armstrong <neil.armstrong@...aro.org>,
 Jessica Zhang <quic_jesszhan@...cinc.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>, dri-devel@...ts.freedesktop.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH 2/4] dt-bindings: display: panel: Add Himax HX83112B

On 23/02/2025 16:29, Luca Weiss wrote:
> Hi Krzysztof,
> 
> On 23-02-2025 12:54 p.m., Krzysztof Kozlowski wrote:
>> On Sat, Feb 22, 2025 at 06:58:05PM +0100, Luca Weiss wrote:
>>> Himax HX83112B is a display driver IC used to drive LCD DSI panels.
>>> Describe it and the Fairphone 3 panel from DJN using it.
>>>
>>> Signed-off-by: Luca Weiss <luca@...aweiss.eu>
>>> ---
>>>   .../bindings/display/panel/himax,hx83112b.yaml     | 75 ++++++++++++++++++++++
>>>   1 file changed, 75 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/display/panel/himax,hx83112b.yaml b/Documentation/devicetree/bindings/display/panel/himax,hx83112b.yaml
>>> new file mode 100644
>>> index 0000000000000000000000000000000000000000..e6bd4b33d40be98e479d84617aea6d2af0df70e4
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/display/panel/himax,hx83112b.yaml
>>> @@ -0,0 +1,75 @@
>>> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
>>> +%YAML 1.2
>>> +---
>>> +$id: http://devicetree.org/schemas/display/panel/himax,hx83112b.yaml#
>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>> +
>>> +title: Himax HX83112B-based DSI display panels
>>> +
>>> +maintainers:
>>> +  - Luca Weiss <luca@...aweiss.eu>
>>> +
>>> +description:
>>> +  The Himax HX83112B is a generic DSI Panel IC used to control
>>> +  LCD panels.
>>> +
>>> +allOf:
>>> +  - $ref: panel-common.yaml#
>>> +
>>> +properties:
>>> +  compatible:
>>> +    contains:
>>> +      const: djn,fairphone-fp3-panel
>>
>> Why no himax,hx83112b fallback?
> 
> While this is the driver IC for this panel, I don't think there's any 
> "generic" init sequence that can successfully configure this panel, so 
> generic hx83112b driver could work I'd say.


Hm, indeed usually this would mean no need for unusable fallback alone,
but still drivers could use it for some common pieces of code. I imagine
there could be a piece of init sequence which is generic. Or some piece
of attributes.
We already have examples of both approaches for panels - with generic
fallback (himax,hx83102) and without (himax,hx83112a).

@Rob
what is your generic advice? Which of above (himax,hx83102 vs
himax,hx83112a) should be used, if the fallback compatible cannot be
used alone?

Best regards,
Krzysztof