[Letux-kernel] jz4730 sound

[Paul Boddie]

On Saturday, 23 January 2021 18:22:46 CET H. Nikolaus Schaller wrote:
> Hi Paul,
> I have found some issues in the device tree and
> the i2s node wasn't complete at all.

Sorry not to reply to this earlier! To look into this a bit more, I reviewed 
the clock definitions and found that we were missing a "bitclk" for AIC/I2S, 
and the gating wasn't being done for the existing I2S clock. So, there's a 
patch to add a new clock and to update the existing one.

> Hence I have checked with jz4740 and the i2s controllers
> are quite similar. On a first scan of the documentation
> there are only minor differences in 24 bit capabilites.
> And some status registers may have additional bits.

It will probably need checking just to make sure.

> So it is likely to get it run.
> 
> But it needs DMA...
> And I2C to access the external sound chip...

I hadn't looked into interacting with the sound chip over I2C, not really 
knowing where to start, but we will obviously need reliable I2C support to 
have a chance of setting it up.

> Maybe it is also easier to test DMA for this subsystem
> than for MMC which is necessary for boot.

Yes, I would imagine so.

> Anyways, attached is a proposal where I think the compatible,
> the ref and the interrupt and dma channel numbers are correct.
> 
> What do you think how to correctly set up the jz4730 clocks?

The patch should fix the clocks to make them available. About the node 
itself...

> 	i2s: i2s at 10020000 {
> 		compatible = "ingenic,jz4730-i2s";

I guess we will only need JZ4730-specific identification if there are some 
differences, but you probably know more about this than me at the moment. :-)

> 		reg = <0x10020000 0x38>;
> 
> 		#sound-dai-cells = <0>;
> 
> 		interrupt-parent = <&intc>;
> 		interrupts = <20>;
> 
> /* FIXME:
> 		clocks = <&cgu JZ4740_CLK_AIC>,
> 			 <&cgu JZ4740_CLK_I2S>,
> 			 <&cgu JZ4740_CLK_EXT>,
> 			 <&cgu JZ4740_CLK_PLL_HALF>;
> 		clock-names = "aic", "i2s", "ext", "pll half";
> */

This looks OK. I add the missing AIC clock in the patch, which is the 
"bitclk".

> 		dmas = <&dmac 25 0xffffffff>, <&dmac 24 0xffffffff>;
> 		dma-names = "rx", "tx";
> 	};

I hope this is OK, too!

Paul
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