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

[Robert Foss]

Hey Gary,

On 4/10/19 9:35 AM, Gary Bisson wrote:
> Hi,
>
> On Tue, Apr 9, 2019 at 2:07 AM Robert Foss <robert.foss@xxxxxxxxxxxxx> wrote:
> > Hey Fabio,
> >
> > On 4/8/19 10:37 PM, Fabio Estevam wrote:
> > > Hi Robert,
> > >
> > > [Adding Gary]
>
> Adding Troy, I'm no longer a full-time employee at Boundary Devices.
>
> > > On Mon, Apr 8, 2019 at 2:54 PM Robert Foss <robert.foss@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > > > ---
> > > >    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.
>
> Does this happen if the LVDS is disabled in cmdline? (adding "video=LVDS-1:d")

I hadn't tried this before, but is seems yo yield the same results

# cat /proc/cmdline
video=LVDS-1:d enforcing=0 ip=dhcp rw rootwait root=/dev/mmcblk1p1 
log_buf_len=16M cma=512M vmalloc=512M

# dmesg
imx-drm display-subsystem: failed to bind disp0 (ops imx_pd_ops): -517
imx-drm display-subsystem: master bind failed: -517

This dmesg log is failing to bind disp0 at another point than what I
was seeing before, yet the result is the same. The connected HDMI
output is not brought online correctly.

> Note that a bootscript was written for mainline kernel that takes care
> of display configuration [1].
>
> Currently this bootscript disables all the displays that aren't used.
> It was tested with HDMI, where LVDS and LCD display are disabled, and
> it *used to* work.
>
> If this doesn't work then there's most likely a regression somewhere.
>
> Regards,
> Gary
>
> [1] https://github.com/boundarydevices/u-boot-imx6/blob/boundary-v2018.07/board/boundary/bootscripts/bootscript-mainline.txt#L90
>
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