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

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Message-ID: <CAL_JsqJ=T0p17hHg6=obtydt7T-yrAeOr7C2XAEnDFQ-c0b5XQ@mail.gmail.com>
Date:   Thu, 31 May 2018 09:20:57 -0500
From:   Rob Herring <robh@...nel.org>
To:     Codrin Ciubotariu <codrin.ciubotariu@...rochip.com>
Cc:     "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org, linux-clk <linux-clk@...r.kernel.org>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Mark Brown <broonie@...nel.org>, Cristian.Birsan@...rochip.com
Subject: Re: [PATCH v4 1/7] dt-bindings: clk: at91: add an I2S mux clock

On Thu, May 31, 2018 at 5:25 AM, Codrin Ciubotariu
<codrin.ciubotariu@...rochip.com> wrote:
> 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.

Ah, now I remember. AT91 uses fine grained clock nodes in DT. Is there
still a plan to fix this?

>>>     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.

I wasn't suggesting a clock-id property, but a clock specifier (i.e.
make #clock-cells 1).

But AT91 clocks are all a mess, so I don't know what to tell you.

Rob