Re: [v3, 4/5] powerpc: dts: t4240: add syscon support for DCFG node

[Scott Wood <scottwood@freescale.com>]

On Fri, 2015-11-27 at 11:20 +0800, Yangbo Lu wrote:
> Add syscon support for DCFG node, so that the driver could use
> syscon regmap interface to access the device config module registers.
> And the CONFIG_MFD_SYSCON should be enabled for this.
> 
> Signed-off-by: Yangbo Lu <yangbo.lu@freescale.com>
> ---
> Changes for v2:
> 	- None
> Changes for v3:
> 	- Added this patch
> ---
>  arch/powerpc/boot/dts/fsl/t4240si-post.dtsi | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/boot/dts/fsl/t4240si-post.dtsi
> b/arch/powerpc/boot/dts/fsl/t4240si-post.dtsi
> index 68c4ead..5f148b2 100644
> --- a/arch/powerpc/boot/dts/fsl/t4240si-post.dtsi
> +++ b/arch/powerpc/boot/dts/fsl/t4240si-post.dtsi
> @@ -941,7 +941,9 @@
>  /include/ "qoriq-mpic4.3.dtsi"
>  
>  	guts: global-utilities@e0000 {
> -		compatible = "fsl,t4240-device-config", "fsl,qoriq-device
> -config-2.0";
> +		compatible = "fsl,t4240-device-config",
> +				"fsl,qoriq-device-config-2.0",
> +				"syscon";


I really don't like changing the device tree based on Linux internals.  It
also means that the workaround wouldn't work for users that don't upgrade
their device tree.  I definitely don't like one QorIQ chip having "syscon" on
the dcfg node but others not having it.

The guts driver should just maintain a list of compatibles to match.  Why do
we need to use syscon, rather than a guts driver that exports an fsl_get_svr()
function?

-Scott