Re: [PATCH] ARM: dts: imx6qdl-nitrogen6_max: Disable LVDS channels

From: Robert Foss <robert.foss@collabora.com>
To: Fabio Estevam <festevam@gmail.com>,
	Gary Bisson <gary.bisson@boundarydevices.com>
Cc: Shawn Guo <shawnguo@kernel.org>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	Sascha Hauer <kernel@pengutronix.de>,
	Fabio Estevam <fabio.estevam@nxp.com>,
	NXP Linux Team <linux-imx@nxp.com>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	"moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
	<linux-arm-kernel@lists.infradead.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ARM: dts: imx6qdl-nitrogen6_max: Disable LVDS channels
Date: Tue, 9 Apr 2019 02:07:25 +0200	[thread overview]
Message-ID: <4fd506a1-c961-0569-6d39-283758f363d9@collabora.com> (raw)
In-Reply-To: <CAOMZO5DAvaibi5r9CXzk8qbE7XHiHJHHvi9rcq_BJdx7aRVgoQ@mail.gmail.com>

Hey Fabio,

On 4/8/19 10:37 PM, Fabio Estevam wrote:
> Hi Robert,
> 
> [Adding Gary]
> 
> On Mon, Apr 8, 2019 at 2:54 PM Robert Foss <robert.foss@collabora.com> wrote:
>>
>> If a LVDS device is not connected, having the LVDS channels
>> enabled will prevent imx-ldb from probing correctly even
>> if other CRTCs are connected.
>>
>> Signed-off-by: Robert Foss <robert.foss@collabora.com>
>> ---
>>   arch/arm/boot/dts/imx6qdl-nitrogen6_max.dtsi | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm/boot/dts/imx6qdl-nitrogen6_max.dtsi b/arch/arm/boot/dts/imx6qdl-nitrogen6_max.dtsi
>> index 39200e5dc896..5b413cf4c250 100644
>> --- a/arch/arm/boot/dts/imx6qdl-nitrogen6_max.dtsi
>> +++ b/arch/arm/boot/dts/imx6qdl-nitrogen6_max.dtsi
>> @@ -703,7 +703,7 @@
>>          status = "okay";
>>
>>          lvds-channel@0 {
>> -               status = "okay";
>> +               status = "disabled";
>>
>>                  port@4 {
>>                          reg = <4>;
>> @@ -715,7 +715,7 @@
>>          };
>>
>>          lvds-channel@1 {
>> -               status = "okay";
>> +               status = "disabled";
> 
> I am not sure I understood what you are trying to fix.

If CONFIG_DRM_IMX_LDB is enabled, LVDS DT channels are enabled
and no LVDS-panels are connected the imx-ldb driver will
fail to bind.

This is a problem, since it will prevent other actually connected
display output from being used, even if they bind properly.

> 
> Could you please share some logs when imx-ldb fails to probe correctly?

[    2.119563] component_bind_all() trying to bind: ldb
[    2.124600] imx-drm display-subsystem: binding ldb (ops imx_ldb_ops)
[    2.146169] drm_of_find_panel_or_bridge() np->name=lvds-channel  np->type=<NULL>
[    2.153709] drm_of_find_panel_or_bridge() no panel found for remote
[    2.160081] drm_of_find_panel_or_bridge() bridge needed
[    2.162043] drm_of_find_panel_or_bridge() bridge not found
[    2.165331] drm_of_find_panel_or_bridge() failed
[    2.170023] imx-drm display-subsystem: failed to bind ldb (ops imx_ldb_ops): -517

This at the same time as HDMI binds properly:

[    4.458954] dwhdmi-imx 120000.hdmi: Detected HDMI TX controller v1.30a with 
HDCP (DWC HDMI 3D TX PHY)
[    4.469633] imx-drm display-subsystem: bound 120000.hdmi (ops dw_hdmi_imx_ops)

Which in the end causes the IMX driver to not initialize properly
and ignore the HDMI connection that bound properly.
This in turn prevents us from having any graphical output while there
is no LVDS panel connected.

> 
> Is this a regression?
> 

Not as far as I know.

How a Nitrogen6-Max board without a LVDS panel, but using the
imx_v6_v7_defconfig ever started and had displayed graphical
output on other connected displays I don't know though.

Rob.