Re: [PATCH 1/7] ARM: dts: imx: keep the SY7636A VCOM on

[Andreas Kemnade]

On Tue, 10 Nov 2026 15:23:03 +1000
Alistair <alistair@xxxxxxxxxxxxx> wrote:

> On Mon, 2026-10-26 at 08:30 +0100, Andreas Kemnade wrote:
> > On Mon, 26 Oct 2026 00:39:12 +0000
> > Pablo Mazzini <pmazzini@xxxxxxxxx> wrote:
> >   
> > > The SY7636A hwmon driver turns VCOM on at probe. The reMarkable 2,
> > > Kobo
> > > Libra H2O and Tolino Vision 5 have had the rails on so far. Mark
> > > VCOM
> > > always-on before the driver stops doing it.
> > > 
> > > Signed-off-by: Pablo Mazzini <pmazzini@xxxxxxxxx>
> > > ---
> > >  arch/arm/boot/dts/nxp/imx/e70k02.dtsi           | 1 +
> > >  arch/arm/boot/dts/nxp/imx/imx7d-remarkable2.dts | 1 +
> > >  2 files changed, 2 insertions(+)
> > > 
> > > diff --git a/arch/arm/boot/dts/nxp/imx/e70k02.dtsi
> > > b/arch/arm/boot/dts/nxp/imx/e70k02.dtsi
> > > index dc7ff108aa85..bd9c6c6fa117 100644
> > > --- a/arch/arm/boot/dts/nxp/imx/e70k02.dtsi
> > > +++ b/arch/arm/boot/dts/nxp/imx/e70k02.dtsi
> > > @@ -154,6 +154,7 @@ sy7636: pmic@62 {
> > >  		regulators {
> > >  			reg_epdpmic: vcom {
> > >  				regulator-name = "vcom";
> > > +				regulator-always-on;
> > >  			};
> > >  		};
> > >  	};  
> > No, please not. That regulator is in practice used with a not yet
> > upstreamed
> > driver for the EPDC on that platform used to deal with the current
> > kernels
> > fp9931 / tps65185 drivers. So it is very welcome to have it not
> > always turned
> > on.
> > 
> >   
> > > diff --git a/arch/arm/boot/dts/nxp/imx/imx7d-remarkable2.dts
> > > b/arch/arm/boot/dts/nxp/imx/imx7d-remarkable2.dts
> > > index ff9d50942884..6cf5603c0752 100644
> > > --- a/arch/arm/boot/dts/nxp/imx/imx7d-remarkable2.dts
> > > +++ b/arch/arm/boot/dts/nxp/imx/imx7d-remarkable2.dts
> > > @@ -327,6 +327,7 @@ sy7636a: pmic@62 {
> > >  		regulators {
> > >  			reg_epdpmic: vcom {
> > >  				regulator-name = "vcom";
> > > +				regulator-always-on;
> > >  				regulator-boot-on;
> > >  			};
> > >  		};  
> > 
> > 
> > Here the situation is a bit different. If I remember correctly, there
> > is some special EPD logic in userspace on top of some ordinary kernel
> > display driver. But thesse things are missing is devicetree?! But  
> 
> Yeah, the kernel just exposes a framebuffer and a special secret sauce
> userspace program writes to that.

Looking at that processor. It seems to have an EPDC like the i.MX6 has.
Looking even further. The Kobo factory kernel for i.MX6SLL devices specifies
fsl,imx7d-epdc as compatible for that.
So if your display is just connected to that EPDC, then you could probably
wire up things on top of my EPDC driver with DRM interface.

So you still too need to run your own fork for the display? 

> 
> > that might need to learn to deal with regulator enabling/disabling.
> > 
> > Regulator always on is probably not desired here, either.  
> 
> Yeah, I **think** we don't need that
> 
You just need to add logic to enable/disable the regulator (if it is not
wired up yet). But it is nothing from the perspective of mainline to worry
about.

Regards,
Andreas