linux-kernel - Re: [PATCH 1/3] dt-bindings: drm/bridge: ti-sn65dsi83: Add optional property ti,lvds-vcom

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Message-ID: <20241128-mottled-nostalgic-oriole-be31ce@houat>
Date: Thu, 28 Nov 2024 11:29:20 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Andrej Picej <andrej.picej@...ik.com>
Cc: Rob Herring <robh@...nel.org>, andrzej.hajda@...el.com, 
	neil.armstrong@...aro.org, rfoss@...nel.org, Laurent.pinchart@...asonboard.com, 
	jonas@...boo.se, jernej.skrabec@...il.com, airlied@...il.com, simona@...ll.ch, 
	maarten.lankhorst@...ux.intel.com, tzimmermann@...e.de, krzk+dt@...nel.org, conor+dt@...nel.org, 
	shawnguo@...nel.org, s.hauer@...gutronix.de, kernel@...gutronix.de, 
	festevam@...il.com, marex@...x.de, dri-devel@...ts.freedesktop.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, imx@...ts.linux.dev, 
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/3] dt-bindings: drm/bridge: ti-sn65dsi83: Add optional
 property ti,lvds-vcom

On Thu, Nov 28, 2024 at 09:46:33AM +0100, Andrej Picej wrote:
> On 27. 11. 24 16:16, Rob Herring wrote:
> > On Wed, Nov 27, 2024 at 11:30:29AM +0100, Andrej Picej wrote:
> > > From: Janine Hagemann <j.hagemann@...tec.de>
> > > 
> > > Add an optional property to change LVDS output voltage. This depends on
> > > the connected display specifications. With this property we directly set
> > > the LVDS_VCOM (0x19) register.
> > > Better register property mapping would be quite tricky. Please check
> > > bridge's datasheet for details on how register values set the LVDS
> > > data lines and LVDS clock output voltage.
> > > 
> > > Signed-off-by: Janine Hagemann <j.hagemann@...tec.de>
> > > Signed-off-by: Andrej Picej <andrej.picej@...ik.com>
> > > ---
> > >   .../bindings/display/bridge/ti,sn65dsi83.yaml      | 14 +++++++++++++-
> > >   1 file changed, 13 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi83.yaml b/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi83.yaml
> > > index 48a97bb3e2e0..5b2c0c281824 100644
> > > --- a/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi83.yaml
> > > +++ b/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi83.yaml
> > > @@ -58,6 +58,12 @@ properties:
> > >                     - const: 2
> > >                     - const: 3
> > >                     - const: 4
> > > +              ti,lvds-vcom:
> > > +                $ref: /schemas/types.yaml#/definitions/uint32
> > > +                description: LVDS output voltage configuration. This defines
> > > +                  LVDS_VCOM (0x19) register value. Check bridge's datasheet for
> > > +                  details on how register values set the LVDS data lines and
> > > +                  LVDS clock output voltage.
> > 
> > Constraints? 0 - 2^32 are all valid values?
> 
> Not really, only first 6 bits, which also means that this can be uint8 then.
> Will fix with other issues.

Also, generally speaking directly using register values is really
frowned upon, even more so when they match a value expressed in a
standard unit.

Maxime

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