Re: [PATCH] clk: si5351: Apply PLL soft reset before enabling the outputs

[Sergej Sawazki <sergej@taudac.com>]

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Am 26.07.2017 um 06:43 schrieb Sebastian Hesselbarth:
> On 26.07.2017 03:11, Stephen Boyd wrote:
>> On 07/25, Sergej Sawazki wrote:
>>> The "Si5351A/B/C Data Sheet" states to apply a PLLA and PLLB soft reset
>>> before enabling the outputs [1]. This is required to get a deterministic
>>> phase relationship between the output clocks.
>>>
>>> Without the PLL reset, the phase offset beween the clocks is unpredictable.
>>>
>>> References:
>>> [1] https://www.silabs.com/Support%20Documents/TechnicalDocs/Si5351-B.pdf
>>>     Figure 12 ("I2C Programming Procedure")
>>>
>>> Cc: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
>>> Cc: Rabeeh Khoury <rabeeh@solid-run.com>
>>> Signed-off-by: Sergej Sawazki <sergej@taudac.com>
>>> ---
>> This is similar to commit 6dc669a22c77 (clk: si5351: Add PLL soft
>> reset, 2015-11-20)? But I think that commit was causing some
>> problem for Russell King and there was going to be a patch to
>> change it but nothing has materialized on the list. Unless this
>> is that patch?
> Sergej, Stephen,
>
> resetting both PLLs in this driver will not happen as it does have
> an influence on the other PLL and all clocks on it.
>
> I understand that some of the functions of the clk gen will not be
> available with this driver but it is not the use case of this driver.
>
> So, NAK on this one.
>
> The patch you are talking about is still pending but I think I just
> send it in a few days.
>
> Sebastian

Sebastian, Stephen,

On my setup, the Si5351 provides audio bit and frame clocks. Without
resetting the PLLs before enabling the output clocks the phase offset
between the clocks is unpredictable, the clocks are not aligned, this
corrupts the audio stream.

I agree, resetting both PLLs is not a good idea. Only one PLL should
be resetted (the one that the output clocks are connected to).

I am not changing the rates, I am only enabling/disabling the outputs
and changing the clkin source. So resetting the PLL in set_rate() does
not help me.

Sergej

 

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