linux-kernel - Re: [RFC PATCH 01/10] dt-bindings: soc: imx-blk-ctrl: add 'fsl,power-domains-boot-on' property

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Message-ID: <20241101173914.GA3786619-robh@kernel.org>
Date: Fri, 1 Nov 2024 12:39:14 -0500
From: Rob Herring <robh@...nel.org>
To: Dario Binacchi <dario.binacchi@...rulasolutions.com>
Cc: linux-kernel@...r.kernel.org, linux-amarula@...rulasolutions.com,
	Conor Dooley <conor+dt@...nel.org>,
	Fabio Estevam <festevam@...il.com>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Lucas Stach <l.stach@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Shawn Guo <shawnguo@...nel.org>, devicetree@...r.kernel.org,
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH 01/10] dt-bindings: soc: imx-blk-ctrl: add
 'fsl,power-domains-boot-on' property

On Mon, Oct 28, 2024 at 11:25:24AM +0100, Dario Binacchi wrote:
> This property lists the state of the power domains, indicating whether
> they have been left on or off by the bootloader/firmware.
> This information becomes relevant, for example, in the case of supporting
> the simple framebuffer.
> 
> Signed-off-by: Dario Binacchi <dario.binacchi@...rulasolutions.com>
> ---
> 
>  .../bindings/soc/imx/fsl,imx8mn-disp-blk-ctrl.yaml       | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/soc/imx/fsl,imx8mn-disp-blk-ctrl.yaml b/Documentation/devicetree/bindings/soc/imx/fsl,imx8mn-disp-blk-ctrl.yaml
> index eeec9965b091..00aa0b8d8ea9 100644
> --- a/Documentation/devicetree/bindings/soc/imx/fsl,imx8mn-disp-blk-ctrl.yaml
> +++ b/Documentation/devicetree/bindings/soc/imx/fsl,imx8mn-disp-blk-ctrl.yaml
> @@ -56,6 +56,15 @@ properties:
>        - const: csi-aclk
>        - const: csi-pclk
>  
> +  fsl,power-domains-boot-on:
> +    description: |
> +      Provide the on/off (1/0) status of the power domains. It allows
> +      specifying whether one or more power domains have already been
> +      initialized and left powered on by the bootloader.

Sounds like a common problem *if* we wanted to fix it in DT.

Why can't you just read the h/w registers to see which domains are 
powered on? Perhaps because some are on, but you want to turn them off.

Also, for simple-framebuffer, I think you can list the power-domains to 
keep on.

Rob