linux-kernel - Re: [V2 1/2] clk: imx6q: remove unsupported pll4_audio

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Date:   Mon, 11 Mar 2019 13:48:55 -0700
From:   Eric Nelson <eric@...int.com>
To:     devicetree@...r.kernel.org, linux-clk@...r.kernel.org
Cc:     anson.huang@....com, colin.didier@...ialet.com, festevam@...il.com,
        kernel@...gutronix.de, l.stach@...gutronix.de,
        linux-arm-kernel@...ts.infradead.org, linux-imx@....com,
        linux-kernel@...r.kernel.org, mark.rutland@....com,
        mturquette@...libre.com, robh+dt@...nel.org,
        s.hauer@...gutronix.de, sboyd@...nel.org, shawnguo@...nel.org,
        tiny.windzz@...il.com
Subject: Re: [V2 1/2] clk: imx6q: remove unsupported pll4_audio_div

 > On March 11, 2019, 6:35 p.m. UTC, Stephen Boyd wrote:
 >
> Quoting Eric Nelson (2019-03-11 08:59:56)
>> diff --git a/include/dt-bindings/clock/imx6qdl-clock.h b/include/dt-bindings/clock/imx6qdl-clock.h
>> index b3cef29..34bb14d 100644
>> --- a/include/dt-bindings/clock/imx6qdl-clock.h
>> +++ b/include/dt-bindings/clock/imx6qdl-clock.h
>> @@ -213,7 +213,15 @@
>>  #define IMX6QDL_CLK_CKO2                       200
>>  #define IMX6QDL_CLK_CKO                                201
>>  #define IMX6QDL_CLK_VDOA                       202
>> -#define IMX6QDL_CLK_PLL4_AUDIO_DIV             203
>> +
>> +/* The PLL4_AUDIO_DIV divider only appeared in
>> + * early versions of the reference manual.
>> + *
>> + * Renamed to _BROKEN to prevent inadvertent use,
>> + * but reserved the array slot to maintain DT binary
>> + * compatibility.
>> + */
>> +#define IMX6QDL_CLK_PLL4_AUDIO_DIV_BROKEN      203
> 
> But it breaks the build. I don't get it. Just add a comment indicating
> it shouldn't be used? That breaks the cross-tree dependency chain and
> lets clk tree merge the clk driver part and arm-soc merge the dts part.
The device tree update also requires the update to clk-imx6q.c
for proper run-time operation, so I don't see how these two parts
can be separated.

I thought about leaving the PLL4_AUDIO_DIV clock in place but
turning it into a dummy (placeholder), but that might lead others
down the long path I traversed before I found out that my manual
was old and the clock didn't function.