Re: [PATCH 19/25] ARM: tegra: Add dummy backlight power supplies

Thierry Reding
2021-12-10T14:51:47Z

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On Thu, Dec 09, 2021 at 10:07:48PM +0300, Dmitry Osipenko wrote:
> 09.12.2021 20:33, Thierry Reding пишет:
> > From: Thierry Reding <treding@nvidia.com>
> >
> > The Medcom Wide and PAZ00 boards don't specify the power supply for the
> > backlight, which means that the Linux driver will provide a dummy one.
> > Wire up an explicit dummy to also make the DT schema validation succeed.
> > Unfortunately I don't have access to the schematics for these boards, so
> > I don't know if a more accurate description is possible.
> >
> > Signed-off-by: Thierry Reding <treding@nvidia.com>
> > ---
> > arch/arm/boot/dts/tegra20-medcom-wide.dts | 3 +++
> > arch/arm/boot/dts/tegra20-paz00.dts | 3 +++
> > 2 files changed, 6 insertions(+)
> >
> > diff --git a/arch/arm/boot/dts/tegra20-medcom-wide.dts b/arch/arm/boot/dts/tegra20-medcom-wide.dts
> > index ed0e4012e140..b072d715999e 100644
> > --- a/arch/arm/boot/dts/tegra20-medcom-wide.dts
> > +++ b/arch/arm/boot/dts/tegra20-medcom-wide.dts
> > @@ -54,6 +54,9 @@ backlight: backlight {
> >
> > brightness-levels = <0 4 8 16 32 64 128 255>;
> > default-brightness-level = <6>;
> > +
> > + /* dummy */
> > + power-supply = <&vdd_5v0_reg>;
> > };
> >
> > panel: panel {
> > diff --git a/arch/arm/boot/dts/tegra20-paz00.dts b/arch/arm/boot/dts/tegra20-paz00.dts
> > index e4c6c1363fc5..dd80108ac72c 100644
> > --- a/arch/arm/boot/dts/tegra20-paz00.dts
> > +++ b/arch/arm/boot/dts/tegra20-paz00.dts
> > @@ -571,6 +571,9 @@ backlight: backlight {
> >
> > brightness-levels = <0 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240 255>;
> > default-brightness-level = <10>;
> > +
> > + /* dummy */
> > + power-supply = <&p5valw_reg>;
> > };
> >
> > clk32k_in: clock-32k {
> >
>
> I think David's patches should be more correct [1][2]. Very unlikely
> that 5v is used directly for backlight. I looked at the AC100 patch
> previously, checking schematics. You can download paz00 schematics from
> the internet [3].
>
> [1]
> https://github.com/okias/linux/commit/0a24a3097b2dcb6bb81b13197a2d4836f858199e
>
> [2]
> https://github.com/okias/linux/commit/98a2a32c482d0ffd59d96d22ae4169cc3d0ff15d
>
> [3]
> https://www.s-manuals.com/pdf/motherboard/compal/compal_la-6352p_r1.0a_schematics.pdf

It's not really clear from that schematic which one exactly drives the
backlight, but vdd_pnl_reg is probably close enough. And yeah,
vdd_3v3_reg on Medcom Wide is likely a bit better. I'll pick those
instead and credit David for it.

Thanks for the pointer.

Thierry

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