[alsa-devel] ASoC: new ac97 bus and codec clock

[Mark Brown]

On Sun, Jun 17, 2018 at 10:03:54PM +0200, Robert Jarzmik wrote:

> The new ac97 is working well in a platform data build. But in the device tree
> case, there is an issue, triggered by our review in [1].

> The main issue is the lack of one clock.

> The device hierarchy is :
>  - platform device sound at 40500000 (the AC97 controller)
>    \-> ac97 device sound at 40500000:0 (the discovered ac97 IP for a wm9713)

> Now the issue is here :
>  - sound/ac97/bus.c:419, function ac97_get_enable_clk()
>  - the clk_get() fails

> The sound at 40500000:0 device was automatically created by the AC97 bus code, but
> I don't see any way to provide this device the "ac97_clk" ... How do you think
> this is supposed to work, and how can my devicetree description provide this
> clock ?

This sounds like a DT question - how do you hook things up using DT to a
device that will be enumerated from the hardware?  I'm not sure what
best practice is here, adding Rob and Frank.

> [1] Discussion reference
> https://groups.google.com/forum/#!msg/linux.kernel/6_zIXK_maA4/RMYsmLlRMgAJ
> Look for "You probably mean the BITCLK clock."
> 
> [2] Device tree extract
> ac97: sound at 40500000 {
>       	compatible = "marvell,pxa270-ac97";
> 	reg = < 0x40500000 0x1000 >;
> 	interrupts = <14>;
> 	reset-gpios = <&gpio 95 GPIO_ACTIVE_HIGH>;
> 	#sound-dai-cells = <1>;
> 	pinctrl-names = "default";
> 	pinctrl-0 = < &pinctrl_ac97_default >;
> 	clocks = <&clks CLK_AC97>, <&clks CLK_AC97CONF>;
> 	clock-names = "AC97CLK", "AC97CONFCLK";
> };
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