> Subject: [PATCH 1/2] Powerpc: Add voltage ranges support for T4
>
> Special voltages that can be support by eSDHC of T4 in esdhc node.
>
> Signed-off-by: Haijun Zhang <[email protected]>
> Signed-off-by: Anton Vorontsov <[email protected]>
> --- a/Documentation/devicetree/bindings/mmc/fsl-esdhc.txt
> +++ b/Documentation/devicetree/bindings/mmc/fsl-esdhc.txt
> @@ -19,6 +19,8 @@ Optional properties:
> "bus-width = <1>" property.
> - sdhci,auto-cmd12: specifies that a controller can only handle auto
> CMD12.
> + - 3300 3300: specifies that eSDHC controller can support voltages
> ranges
> + from 3300 to 3300. This is an optional.
"This is an optional." is an unclear statement.
> +++ b/arch/powerpc/boot/dts/fsl/t4240si-post.dtsi
> @@ -399,6 +399,7 @@
> sdhc@114000 {
> compatible = "fsl,t4240-esdhc", "fsl,esdhc";
> sdhci,auto-cmd12;
> + voltage-ranges = <1800 1800 3300 3300>;
This is IMHO incorrect and potentially dangerous.
The T4 silicon will only support 1.8V on SDHC pins per hardware specification.
The Freescale T4240QDS reference board has extra voltage shifters added to
allow 3.3V operation, but that is _not_ a silicon feature. It is a specific
board feature that may or may not translate to other boards, depending on how
SD spec conformant a board builder wants to be.
If the intent is to state that a physical SDHC interface on a board has to be
built to support 3.3V operation to be SD spec conformant for off-the-shelf
cards because a reset would change the signal voltage to 3.3V, then I am not
sure that putting this down as silicon "feature" without further explanation
about the background anywhere is the right way to go.
IMHO silicon features are really just silicon features and not technically
optional external circuitry additions implied by common use.
Best regards,
Heinz
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