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

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Message-ID: <18f6871e-794d-3ea2-487e-32399a8b89b4@microchip.com>
Date:   Thu, 7 Jun 2018 13:30:14 +0300
From:   Codrin Ciubotariu <codrin.ciubotariu@...rochip.com>
To:     Rob Herring <robh@...nel.org>, Stephen Boyd <sboyd@...nel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Mark Brown <broonie@...nel.org>
CC:     <devicetree@...r.kernel.org>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        <Cristian.Birsan@...rochip.com>,
        linux-clk <linux-clk@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 1/7] dt-bindings: clk: at91: add an I2S mux clock

On 31.05.2018 18:56, Rob Herring wrote:
> On Thu, May 31, 2018 at 10:31 AM, Stephen Boyd <sboyd@...nel.org> wrote:
>> Quoting Rob Herring (2018-05-31 07:20:57)
>>> 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?
>>
>> I'm also interested in a plan.
>>
>>>>>
>>>>>> +               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.
>>>
>>
>> If #clock-cells of 1 works then we should go with that. It's still weird
>> that we need random nodes to add more clks, but I guess that's how it's
>> going to be for each at91 clk driver until it changes to be one big
>> provider node.
> 
> Seems to me that clock additions could use a new binding and we start
> with a new driver that handles these few clocks initially. But I
> haven't looked whether both can coexist.

Mark already applied to broonie/sound.git the I2S bindings that have a 
phandle to this clock. If I am to change #clock-cells to 1, I will have 
to change the bindings to include the clock-id.
Which approach should I take now?

Thanks and best regards,
Codrin