linux-kernel - Re: [PATCH v4 1/7] dt-bindings: clk: at91: add an I2S mux clock

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Date:   Thu, 31 May 2018 13:25:26 +0300
From:   Codrin Ciubotariu <codrin.ciubotariu@...rochip.com>
To:     Rob Herring <robh@...nel.org>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-clk@...r.kernel.org>, <alsa-devel@...a-project.org>,
        <nicolas.ferre@...rochip.com>, <boris.brezillon@...tlin.com>,
        <alexandre.belloni@...tlin.com>, <broonie@...nel.org>,
        <Cristian.Birsan@...rochip.com>
Subject: Re: [PATCH v4 1/7] dt-bindings: clk: at91: add an I2S mux clock

On 31.05.2018 03:58, Rob Herring wrote:
> On Fri, May 25, 2018 at 03:34:22PM +0300, Codrin Ciubotariu wrote:
>> The I2S mux clock can be used to select the I2S input clock. The
>> available parents are the peripheral and the generated clocks.
>>
>> Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@...rochip.com>
>> ---
>>   .../devicetree/bindings/clock/at91-clock.txt       | 34 ++++++++++++++++++++++
>>   1 file changed, 34 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/clock/at91-clock.txt b/Documentation/devicetree/bindings/clock/at91-clock.txt
>> index 51c259a..1c46b3c 100644
>> --- a/Documentation/devicetree/bindings/clock/at91-clock.txt
>> +++ b/Documentation/devicetree/bindings/clock/at91-clock.txt
>> @@ -90,6 +90,8 @@ Required properties:
>>   	"atmel,sama5d2-clk-audio-pll-pmc"
>>   		at91 audio pll output on AUDIOPLLCLK that feeds the PMC
>>   		and can be used by peripheral clock or generic clock
>> +	"atmel,sama5d2-clk-i2s-mux":
>> +		at91 I2S clock source selection
> 
> Is this boolean or takes some values. If latter, what are valid values?

This is the compatible string of the clock driver.

> 
>>   
>>   Required properties for SCKC node:
>>   - reg : defines the IO memory reserved for the SCKC.
>> @@ -507,3 +509,35 @@ For example:
>>   			atmel,clk-output-range = <0 83000000>;
>>   		};
>>   	};
>> +
>> +Required properties for I2S mux clocks:
>> +- #size-cells : shall be 0 (reg is used to encode I2S bus id).
>> +- #address-cells : shall be 1 (reg is used to encode I2S bus id).
>> +- name: device tree node describing a specific mux clock.
>> +	* #clock-cells : from common clock binding; shall be set to 0.
>> +	* clocks : shall be the mux clock parent phandles; shall be 2 phandles:
>> +	  peripheral and generated clock; the first phandle shall belong to the
>> +	  peripheral clock and the second one shall belong to the generated
>> +	  clock; "clock-indices" property can be user to specify
>> +	  the correct order.
>> +	* reg: I2S bus id of the corresponding mux clock.
>> +	  e.g. reg = <0>; for i2s0, reg = <1>; for i2s1
>> +
>> +For example:
>> +	i2s_clkmux {
> 
> What is this a child of?

It is a child of PMC node, since both parent clocks are generated by PMC.

> 
>> +		compatible = "atmel,sama5d2-clk-i2s-mux";
>> +		#address-cells = <1>;
>> +		#size-cells = <0>;
> 
> How do you address this block? My guess is you don't because it is just
> part of some other block and you are just creating this node to
> instantiate a driver. Just make the node for the actual h/w block a
> clock provider and define the clock ids (0 and 1).

This block is not addressed, but its children are. The register we 
access in this driver is not part of other block. It's a SFR register, 
accessed through syscon and it has nothing to do with the I2S IP (see 
SAMA5D2 DS, page 1256, fig. 44-1: I2SC Block Diagram) that is the 
consumer of this clock. Adding a clock-id property in the I2S node would 
be just like v3 of this series, with the difference that we use clock-id 
instead of alias id to set the clock parent, which is not how you 
suggested back then.

Thank you for your review.

Best regards,
Codrin

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