[PATCH 1/2] Powerpc: Add voltage ranges support for T4

[Zhang Haijun-B42677]

Thanks.

Regards
Haijun.


> -----Original Message-----
> From: Kumar Gala [mailto:galak at kernel.crashing.org]
> Sent: Monday, July 22, 2013 10:40 PM
> To: Wrobel Heinz-R39252
> Cc: Zhang Haijun-B42677; linux-mmc at vger.kernel.org; linuxppc-
> dev at lists.ozlabs.org; Wood Scott-B07421; cjb at laptop.org; Fleming Andy-
> AFLEMING; cbouatmailru at gmail.com
> Subject: Re: [PATCH 1/2] Powerpc: Add voltage ranges support for T4
> 
> 
> On Jul 22, 2013, at 4:47 AM, Wrobel Heinz-R39252 wrote:
> 
> >> 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 <haijun.zhang at freescale.com>
> >> Signed-off-by: Anton Vorontsov <cbouatmailru at gmail.com>
> >
> >> --- 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 at 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
> 
> I'd say that the t4240si-post.dtsi should be:
> 
> 	voltage-ranges = <1800 1800>;
> 
> Than have the t4240qds.dts do:
> 
> 	voltage-ranges = <1800 1800 3300 3300>;
> 
> As the 3.3V sounds like a board specific feature.
> 
> [ send this as 2 patches, on for the t4240si-post.dtsi and another for
> the t4240qds.dts ]
[Haijun Wrote:] ok, thanks Heinz and Kumar.
> 
> - k
>