Subject: Re: [alsa-devel] [PATCH v4 resent 1/2] ASoC: fsl: Add S/PDIF CPU DAI driver

From: Sascha Hauer <[email-masked]>
Date: Wed, 14 Aug 2013 11:56:52 +0200

On Wed, Aug 14, 2013 at 04:48:02PM +0800, Nicolin Chen wrote:
> Hi Sascha,
> 
> On Wed, Aug 14, 2013 at 09:50:17AM +0200, Sascha Hauer wrote:
> > > +  - tx-clksrc-names : The names for all available clock sources for tx, which
> > > +  is also being listed in SoC reference manual, ClkSrc_Sel bit of SPDIF_SRPC.
> > > +  And the name list would be different between different SoC. Use 'null' for
> > > +  those unlisted names, and the max number of tx-clksrc-names should be 8.
> > > +
> > > +  - rx-clksrc-names : The names for all available clock sources for rx, which
> > > +  is also being listed in SoC reference manual, TxClk_Source bit of SPDIF_STC.
> > > +  And the name list would be different between different SoC. Use 'null' for
> > > +  those unlisted names, and the max number of rx-clksrc-names should be 16.
> > > +
> > > +Optional properties:
> > > +
> > > +  - rx-clksrc-lock: This is a boolean property. If present, ClkSrc_Sel bit
> > > +  of SPDIF_SRPC would be set a clock source that cares DPLL locked condition.
> > > +
> > > +Example1:
> > > +
> > > +spdif: spdif@02004000 {
> > > +	clocks = <&clks 197>;
> > > +	clock-names = "core";
> > > +	rx-clksrc-lock;
> > > +	rx-clksrc-names =
> > > +		"lock.ext", "lock.spdif", "lock.asrc",
> > > +		"lock.spdif_ext", "lock.esai", "ext",
> > > +		"spdif", "asrc", "spdif_ext", "esai",
> > > +		"lock.mlb", "lock.mlb_phy", "mlb",
> > > +		"mlb_phy";
> > > +	tx-clksrc-names =
> > > +		"xtal", "spdif", "asrc", "spdif_ext",
> > > +		"esai", "ipg", "mlb", "mlb_phy";
> > 
> > I had a hard time understanding what you are doing here.
> > 
> > With this the clk names in arch/arm/mach-imx/clk-imx6q.c become an API
> > between the Kernel and the devicetree. Don't do that.
> > 
> > There is a standardized devicetree binding for clocks. Use it.
>  
> I think I should first explain to you what this part is doing:
> The driver needs to set Clk_source bit for TX/RX to select the 
> clock from a clock mux. The names listed above are those of the 
> clocks connecting to the mux, while they are not only internal 
> clocks which're included in clk-imx6q.c but also external ones,
> an on-board external osc for example.
> 
> The driver does get the clock by using the standard DT binding,
> see the 'clocks = <&clks 197>' above, and then compare this
> obtained clock->name with the name list to decide which value
> should be set to the Clk_source bit.
> 
> ==================================================================
> ClkSrc_Sel from i.MX6Q reference manual:
> 
> Clock source selection, all other settings not shown are reserved:
> 0000 if (DPLL Locked) SPDIF_RxClk else extal
> 0001 if (DPLL Locked) SPDIF_RxClk else spdif_clk
> 0010 if (DPLL Locked) SPDIF_RxClk else asrc_clk
> 0011 if (DPLL Locked) SPDIF_RxClk else spdif_extclk
> 0100 if (DPLL Locked) SPDIF_Rxclk else esai_hckt
> 0101 extal_clk
> 0110 spdif_clk
> 0111 asrc_clk
> 1000 spdif_extclk
> 1001 esai_hckt
> 1010 if (DPLL Locked) SPDIF_RxClk else mlb_clk
> ==================================================================
> 
> So the name list here basically is not being used to obtain a
> clock like what standardized DT binding does but to provide the
> driver a full list to look up which value should be exactly used
> according to the obtained clock.
> 
> I think I should revise the binding doc for these two lists. It 
> might be hard to explain within that kinda short paragraph. 
> 
> Surely, if I misunderstand your point, please correct me. And
> if you have any sage idea, please guide me.

Something like this:

clocks = <&clks 197>, <&clks 3>, <&clks 197>, <&clks 107>, <&clks SPDIF_EXT>,
         <&clks 118>, <&clks 62>, <&clks 139>, <&clks MLB_PHY>
clock-names = "core", "rxtx0", "rxtx1", "rxtx2", "rxtx3", "rxtx4", "rxtx5", "rxtx6", "rxtx7"

This describes the different input clocks to the spdif core and also
gives a hint to the array index (rxtx_n_) to use.

Sascha

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