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Subject: Re: [PATCH v2 2/3] bindings: sound: Add documentation for TI j721e
 EVM (CPB and IVI)
From:   Peter Ujfalusi <peter.ujfalusi@ti.com>
To:     Rob Herring <robh@kernel.org>
CC:     <devicetree@vger.kernel.org>, <alsa-devel@alsa-project.org>,
        <broonie@kernel.org>, <lgirdwood@gmail.com>,
        <linux-kernel@vger.kernel.org>
References: <20200512131633.32668-1-peter.ujfalusi@ti.com>
 <20200512131633.32668-3-peter.ujfalusi@ti.com>
 <20200519222132.GA488519@bogus> <65631db2-5cb2-003a-0526-65d26372616b@ti.com>
Message-ID: <c91d150c-ddcc-214b-0e7d-ee2318be5269@ti.com>
Date:   Thu, 11 Jun 2020 11:59:59 +0300
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Hi Rob,

On 20/05/2020 14.50, Peter Ujfalusi wrote:
>>> +  clocks:
>>> +    items:
>>> +      - description: PLL4 clock
>>> +      - description: PLL15 clock
>>> +      - description: McASP10 auxclk clock
>>> +      - description: PLL4_HSDIV0 parent for McASP10 auxclk (for 48KH=
z)
>>> +      - description: PLL15_HSDIV0 parent for McASP10 auxclk (for 44.=
1KHz)
>>> +      - description: AUDIO_REFCLK2 clock
>>> +      - description: PLL4_HSDIV2 parent for AUDIO_REFCLK2 clock (for=
 48KHz)
>>> +      - description: PLL15_HSDIV2 parent for AUDIO_REFCLK2 clock (fo=
r 44.1KHz)
>>
>> What h/w are these connected to?
>=20
> These clocks are internal to the SoC with the exception of AUDIO_REFCLK=
2
> which is routed to SoC pin.
>=20
>> You have no control interface here, so how do you have clocks?
>=20
> I need to control these clocks, the sound card is the user of these clo=
cks.
>=20
>> Defining parent clocks seems wrong, too. This seems to just be a=20
>> collection of clocks a driver happens to need. Really, you should be=20
>> able query possible parents and select one with the right frequency=20
>> multiple.
>=20
> The issue in hand is that I need to dynamically switch between certain
> parents of the cpb-mcasp (for McASP) and audio-refclk2 (for the codec)
> based on sampling rate of the stream.
>=20
> The McASP auxclk parent can be selected from 7 source and I must use th=
e
> two dedicated ones.
> The REFCLK2 parent can be selected from 30 source.
>=20
> It is also a limitation of the system that I can not query directly the=

> PLL4/PLL15 frequencies, I can only get the frequency on the HSDIVs, but=

> I can not get the divider on them.
> In order to handle the constraints on clocking I need to know the sourc=
e
> rate so the dividers can be taken into account. The codec is picky when=

> it comes to clocking and there is a need to switch between
> 256/512/768xFS based SCKI in order to be able to support sampling rates=
=2E
>=20
> At the moment I have fixed clocks in place for the pll4/15 with the
> rates they are configured so the dts can switch to a real clock which I=

> can use in the future.
> As things are it is unlikely that I will ever going to have access to
> them, but I wanted to avoid in the bindings:
> ti,j721e-pll4-rate =3D <1179648000>;
> ti,j721e-pll15-rate =3D <1083801600>;
>=20
>>> +
>>> +  clock-names:
>>> +    items:
>>> +      - const: pll4
>>> +      - const: pll15
>>> +      - const: cpb-mcasp
>>> +      - const: cpb-mcasp-48000
>>> +      - const: cpb-mcasp-44100
>>> +      - const: audio-refclk2
>>> +      - const: audio-refclk2-48000
>>> +      - const: audio-refclk2-44100

It should be better to document the refclk2 (and refclk0 for IVI) clocks
based on it's use, not source:
cpb-codec-scki (sourced from audio_refclk2)
cpb-codec-scki-48000/44100

For the IVI binding it is just s/cpb/ivi in the clock-names.

- P=C3=A9ter

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