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

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Message-ID: <emwpl2e7zpzkm4uea22g4hayz66nk7nxylinsd2stuwlatwdc3@ixkbc2bxbz4p>
Date: Sun, 30 Mar 2025 12:09:18 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Luca Weiss <luca@...aweiss.eu>
Cc: Krzysztof Kozlowski <krzk@...nel.org>,
        ~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 Sat, Mar 29, 2025 at 02:54:27PM +0100, Luca Weiss wrote:
> Hi all,
> 
> On 2/24/25 9:16 AM, Krzysztof Kozlowski wrote:
> > 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?
> 
> I believe this thread is still pending of a resolution, based on the model
> number I've found, I made the compatible "djn,98-03057-6598b-i" for v2, but
> it's still a question whether himax,hx83112b should be part of the
> compatible.

My 2c (note, not a DT maintainer or anything): no, the IC driver doesn't
fully define panel programming, so it should not be used as a fallback
compat.

-- 
With best wishes
Dmitry