Re: [PATCH v3 1/2] dt-bindings: leds: backlight: document the SY7758 6-channel High Efficiency LED Driver

[Daniel Thompson <daniel@riscstar.com>]

On Fri, May 29, 2026 at 03:15:03PM +0100, Daniel Thompson wrote:
> On Fri, May 29, 2026 at 02:50:43PM +0200, Neil Armstrong wrote:
> > On 5/29/26 12:35, Daniel Thompson wrote:
> > > On Fri, May 29, 2026 at 12:16:07PM +0200, Neil Armstrong wrote:
> > So it's not really 2 regulators, and having regulators means the enable
> > signal can be shared and would have regulator characteristics which it hasn't.
>
> Agreed. If the EN pin is merely use as an enable and voltage reference
> then it are not two regulators.
>
> However, it is also *not* vddio-supply and enable-gpios. We don't need
> the board design to check this. The pinout diagram in the datasheet
> should be sufficient!
>
> If you have to activate vddio-supply for the backlight to work on the
> board are you sure you don't just have a misnamed vdd-supply that needs
> to be taken care of? That would make much more sense given the datasheet.

After posting this I figured there is another possibility.

If the host GPIO pin is not capable of delivering the 1mA requires by
the chip then the board designer would have to add a buffer and that
buffer would need a power supply... and that power supply could, in
pinciple, be switchable.

However if that were the case then I don't think the power supply for
the buffer would belong in the bindings for the sy7758 so I'm afraid
whichever way I turn it I can't make vddio-supply make sense.


Daniel.