linux-kernel - Re: [RFC 6/6] dt-bindings: mmc: sdhci-msm: Add clk scaling dt parameters

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Date:   Tue, 29 Oct 2019 11:36:59 -0500
From:   Rob Herring <robh@...nel.org>
To:     Ram Prakash Gupta <rampraka@...eaurora.org>
Cc:     asutoshd@...eaurora.org, stummala@...eaurora.org,
        sayalil@...eaurora.org, vbadigan@...eaurora.org,
        cang@...eaurora.org, ppvk@...eaurora.org, adrian.hunter@...el.com,
        ulf.hansson@...aro.org, linux-mmc@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [RFC 6/6] dt-bindings: mmc: sdhci-msm: Add clk scaling dt
 parameters

On Mon, Oct 21, 2019 at 07:59:37PM +0530, Ram Prakash Gupta wrote:
> Adding clk scaling dt parameters.
> 
> Signed-off-by: Ram Prakash Gupta <rampraka@...eaurora.org>
> ---
>  Documentation/devicetree/bindings/mmc/sdhci-msm.txt | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/mmc/sdhci-msm.txt b/Documentation/devicetree/bindings/mmc/sdhci-msm.txt
> index da4edb1..afaf88d 100644
> --- a/Documentation/devicetree/bindings/mmc/sdhci-msm.txt
> +++ b/Documentation/devicetree/bindings/mmc/sdhci-msm.txt
> @@ -39,6 +39,21 @@ Required properties:
>  	"cal"	- reference clock for RCLK delay calibration (optional)
>  	"sleep"	- sleep clock for RCLK delay calibration (optional)
>  
> +Optional properties:
> +- devfreq,freq-table - specifies supported frequencies for clock scaling.
> +	Clock scaling logic shall toggle between these frequencies based
> +	on card load. In case the defined frequencies are over or below
> +	the supported card frequencies, they will be overridden
> +	during card init. In case this entry is not supplied,
> +	the driver will construct one based on the card
> +	supported max and min frequencies.
> +	The frequencies must be ordered from lowest to highest.

This should be common. Surely we already have something?

> +
> +- scaling-lower-bus-speed-mode - Few hosts can support DDR52 mode at the
> +	same lower system voltage corner as high-speed mode. In such
> +	cases, it is always better to put it in DDR  mode which will
> +	improve the performance without any power impact.

The description sounds like a boolean. Why the string? What are possible 
values?

Also needs a 'qcom' vendor prefix.

> +
>  Example:
>  
>  	sdhc_1: sdhci@...24900 {
> @@ -56,6 +71,10 @@ Example:
>  
>  		clocks = <&gcc GCC_SDCC1_APPS_CLK>, <&gcc GCC_SDCC1_AHB_CLK>;
>  		clock-names = "core", "iface";
> +
> +		devfreq,freq-table = <50000000 200000000>;
> +		scaling-lower-bus-speed-mode = "DDR52"
> +
>  	};
>  
>  	sdhc_2: sdhci@...a4900 {
> -- 
> 1.9.1
>