linux-kernel - Re: [PATCH 1/2] arm64: dts: qcom: Enable lvds panel-DV215FHM-R01 for rb3gen2 industrial mezzanine

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Message-ID: <p6rsi7nmzlk2q2wtnccwx4r7p74zoyeqq7d7pemhiv6tao56o6@6fivz7qrhkgx>
Date: Thu, 13 Nov 2025 11:00:06 -0600
From: Bjorn Andersson <andersson@...nel.org>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Gopi Botlagunta <venkata.botlagunta@....qualcomm.com>, 
	Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	venkata.valluru@....qualcomm.com, jessica.zhang@....qualcomm.com, 
	Yi Zhang <zhanyi@....qualcomm.com>
Subject: Re: [PATCH 1/2] arm64: dts: qcom: Enable lvds panel-DV215FHM-R01 for
 rb3gen2 industrial mezzanine

On Thu, Nov 13, 2025 at 05:45:42AM +0200, Dmitry Baryshkov wrote:
> On Wed, Nov 12, 2025 at 04:07:27PM -0600, Bjorn Andersson wrote:
> > On Wed, Nov 12, 2025 at 10:16:27PM +0200, Dmitry Baryshkov wrote:
> > > On Wed, Nov 12, 2025 at 10:53:36AM -0600, Bjorn Andersson wrote:
> > > > On Wed, Nov 12, 2025 at 05:02:20PM +0200, Dmitry Baryshkov wrote:
> > > > > On Wed, Nov 12, 2025 at 08:18:11PM +0530, Gopi Botlagunta wrote:
> > > > > > Below is the routing diagram of dsi lanes from qcs6490 soc to
> > > > > > mezzanine.
> > > > > > 
> > > > > > DSI0 --> SW1403.4 --> LT9611uxc --> hdmi port
> > > > > >                  |
> > > > > >                   --> SW2700.1 --> dsi connector
> > > > > >                               |
> > > > > >                                --> LT9211c --> LVDS connector
> > > > > > 
> > > > > > Disable hdmi connector for industrial mezzanine and enable
> > > > > > LT9211c bridge and lvds panel node.
> > > > > > LT9211c is powered by default with reset gpio connected to 117.
> > > > > > 
> > > > > > Signed-off-by: Yi Zhang <zhanyi@....qualcomm.com>
> > > > > > Signed-off-by: Gopi Botlagunta <venkata.botlagunta@....qualcomm.com>
> > > > > > ---
> > > > > >  .../qcom/qcs6490-rb3gen2-industrial-mezzanine.dtso | 106 +++++++++++++++++++++
> > > > > >  1 file changed, 106 insertions(+)
> > > > > > 
> > > > > > diff --git a/arch/arm64/boot/dts/qcom/qcs6490-rb3gen2-industrial-mezzanine.dtso b/arch/arm64/boot/dts/qcom/qcs6490-rb3gen2-industrial-mezzanine.dtso
> > > > > > index 619a42b5ef48..cc8ee1643167 100644
> > > > > > --- a/arch/arm64/boot/dts/qcom/qcs6490-rb3gen2-industrial-mezzanine.dtso
> > > > > > +++ b/arch/arm64/boot/dts/qcom/qcs6490-rb3gen2-industrial-mezzanine.dtso
> > > > > > @@ -8,6 +8,112 @@
> > > > > >  #include <dt-bindings/clock/qcom,gcc-sc7280.h>
> > > > > >  #include <dt-bindings/pinctrl/qcom,pmic-gpio.h>
> > > > > >  
> > > > > > +/ {
> > > > > > +
> > > > > > +	hdmi-connector {
> > > > > > +		status = "disabled";
> > > > > > +	};
> > > > > > +
> > > > > > +	panel_lvds: panel-lvds@0 {
> > > > > > +		compatible = "panel-lvds";
> > > > > 
> > > > > Please describe the actual panel using compatible, etc. It's not that
> > > > > this is some generic uknown LVDS panel.
> > > > > 
> > > > 
> > > > I presume the mezzanine doesn't have a panel, so how do we provide the
> > > > description of the mezzanine such that a developer can quickly get up to
> > > > speed with their specific panel connected to it?
> > > > 
> > > > Do we leave this node disabled, just for reference, or do we specify a
> > > > specific panel and then have the developer copy and adopt this to their
> > > > panel?
> > > > 
> > > > The benefit of doing it like that is that we provide a complete example
> > > > and something we can test. But at the same time, If I presume we might
> > > > have users of the mezzanine without an attached LVDS panel?
> > > > 
> > > > > > +		data-mapping = "vesa-24";
> > > > > > +		width-mm = <476>;
> > > > > > +		height-mm = <268>;
> > > > 
> > > > The way this patch is written we certainly have some specific panel in
> > > > mind...
> > > 
> > > It's even mentioned in the subject: BOE DV215FHM-R01. Having a proper
> > > panel compatible is demanded by the panel-lvds bindings.
> > > 
> > 
> > I missed that mention. But that implies then that this isn't "the
> > industrial mezzanine", but "the industrial mezznine with a boe
> > DV215FHM-R01 connected".
> > 
> > Are you saying that this is the way you'd prefer that we handle the
> > mezzanines with capabilities for extension?
> 
> Some time ago, around APQ8064 boards there was a discussion of using
> EDID to identify LVDS panels (in a manner similar to panel-edp).
> 
> Does industrial mezzanine provide EDID support for the panel?
> 

Even if there is EDID in this particular case, the problem still
remains broadly. If we have a mezzanine with a standard connector, but
the non-probable device is connected by the developer at a later stage,
how do we facilitate their experience?

Concretely, the Particle Tachyon has two CSI/DSI connectors compatible
with Rasberry-Pi accessories, I believe RubikPi3 has the same. We have
no idea what DSI panel (or CSI camera) the user might connect, but
there's common board-specifics and boilerplate that a tinkerer need to
put in place.

Regards,
Bjorn

> -- 
> With best wishes
> Dmitry