mstp10 clock bug

[Ben Dooks <ben.dooks@codethink.co.uk>]

William and I have been looking at the clock bug on mstp10_clks
from the sound.git patch which reverts all the clocks [1]

What happens is that when register the node:

> -		mstp10_clks: mstp10_clks@e6150998 {
> -			compatible = "renesas,r8a7790-mstp-clocks", "renesas,cpg-mstp-clocks";
> -			reg = <0 0xe6150998 0 4>, <0 0xe61509a8 0 4>;
> -			clocks = <&p_clk>, <&mstp10_clks R8A7790_CLK_SSI>,
> -				 <&mstp10_clks R8A7790_CLK_SSI>, <&mstp10_clks R8A7790_CLK_SSI>,
> -				 <&mstp10_clks R8A7790_CLK_SSI>, <&mstp10_clks R8A7790_CLK_SSI>,
> -				 <&mstp10_clks R8A7790_CLK_SSI>, <&mstp10_clks R8A7790_CLK_SSI>,
> -				 <&mstp10_clks R8A7790_CLK_SSI>, <&mstp10_clks R8A7790_CLK_SSI>,
> -				 <&mstp10_clks R8A7790_CLK_SSI>;
> -			#clock-cells = <1>;
> -			renesas,clock-indices = <
> -				R8A7790_CLK_SSI R8A7790_CLK_SSI9 R8A7790_CLK_SSI8
> -				R8A7790_CLK_SSI7 R8A7790_CLK_SSI6 R8A7790_CLK_SSI5
> -				R8A7790_CLK_SSI4 R8A7790_CLK_SSI3 R8A7790_CLK_SSI2
> -				R8A7790_CLK_SSI1 R8A7790_CLK_SSI0
> -			>;
> -			clock-output-names > -				"ssi", "ssi9", "ssi8", "ssi7", "ssi6", "ssi5",
> -				"ssi4", "ssi3", "ssi2", "ssi1", "ssi0";
> -		};
>  	};

The ssi5 clock is registered with a parent of ssi5, not ssi as described
in the above node.

This is due to of_clk_get_parent_name() reading the clock-output-names
property and _assuming_ a 1:1 correspondence for the clock index to the
clock-output-names position. In the case of the mstp clocks each of
these nodes has sparse entries, which means the following:

<&mstp10_clks R8A7790_CLK_SSI> R8A7790_CLK_SSI becomes <&mstp10_clks 5>
and the 5th entry in clock-output-names is "ssi5".

This means that the entire machine comes to a halt as the clock layer
tries to create a clock with itself as a parent (never a good idea)

Currently we do not know the best way to fix this.

- we could update the of_clk_get_parent_name() to check the presence of
   renesas,clock-indices which would be a hack.

- allow the clock driver to register a parent name callback, but that
   would assume we never looked up nodes that where not registered yet.

- change all the clock-output-names arrays for rcar dtsi files to have
   null entries where needed, which would be not nice.

- add a new property for mapping numbers to clock indicies and moving
   the renesas,clock-indices to use that (although that would still end
   up causing a number of issues with the clock handling as is)



> https://git.kernel.org/cgit/linux/kernel/git/broonie/sound.git/commit/?h=topic/rcar&idp8d2aa14d1eefef3dd758242787e837485baad7

-- 
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius