linux-kernel - Re: [PATCH 1/2] Documentation: phy: introduce new optional property to specify drive impedance

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Date:   Thu, 05 Jan 2017 12:15:18 +0100
From:   Heiko Stübner <heiko@...ech.de>
To:     Shawn Lin <shawn.lin@...k-chips.com>
Cc:     Kishon Vijay Abraham I <kishon@...com>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-rockchip@...ts.infradead.org,
        Douglas Anderson <dianders@...omium.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] Documentation: phy: introduce new optional property to specify drive impedance

Hi Shawn,

Am Donnerstag, 5. Januar 2017, 17:31:21 schrieb Shawn Lin:
> We need to modify the drive impedance according to the
> different hardware condition. So let's expose this to
> the DT.
> 
> Signed-off-by: Shawn Lin <shawn.lin@...k-chips.com>
> ---
> 
>  Documentation/devicetree/bindings/phy/rockchip-emmc-phy.txt | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/phy/rockchip-emmc-phy.txt
> b/Documentation/devicetree/bindings/phy/rockchip-emmc-phy.txt index
> e3ea557..731aeb9 100644
> --- a/Documentation/devicetree/bindings/phy/rockchip-emmc-phy.txt
> +++ b/Documentation/devicetree/bindings/phy/rockchip-emmc-phy.txt
> @@ -14,6 +14,11 @@ specified by name:
>  		access to it), it is strongly suggested.
>   - clocks: Should have a phandle to the card clock exported by the SDHCI
> driver.
> 
> +Optional Properties:
> +- drive_impedance: Must be one of 33, 40, 50, 66, 100. This property allows
> +	different boards to specify their own drive impedance depending on the
> +	hardware condition.

In what unit are your 33, 40 etc values?

It is recommended that properties should specify their unit, see all the 
properties ending in "-ma", "-ns" and so on and also 
Documentation/devicetree/bindings/property-units.txt

Also properties should use dashes ("-") not underscores.

Judging by the second patch, these are Ohm, so combining the above you 
probably want

	drive-impedance-ohms

as property name.

Also the patch subject is slightly misleading and should probably specify the 
rockchip-emmc as well :-)


Heiko