Re: [PATCH v5 12/19] ASoC: tegra: Add initial parent configuration for audio mclk

From: Dmitry Osipenko
Date: Thu Jan 02 2020 - 11:12:18 EST

02.01.2020 10:03, Sowjanya Komatineni ÐÐÑÐÑ:
> On 12/27/19 1:19 PM, Sowjanya Komatineni wrote:
>> On 12/27/19 6:56 AM, Dmitry Osipenko wrote:
>>> 25.12.2019 20:57, Mark Brown ÐÐÑÐÑ:
>>>> On Mon, Dec 23, 2019 at 12:14:34AM +0300, Dmitry Osipenko wrote:
>>>>> 21.12.2019 01:26, Sowjanya Komatineni ÐÐÑÐÑ:
>>>>>> Tegra PMC clock clk_out_1 is dedicated for audio mclk from Tegra30
>>>>>> through Tegra210 and currently Tegra clock driver does initial parent
>>>>>> configuration for audio mclk "clk_out_1" and enables them by default.
>>>> Please delete unneeded context from mails when replying. Doing this
>>>> makes it much easier to find your reply in the message, helping ensure
>>>> it won't be missed by people scrolling through the irrelevant quoted
>>>> material.
>>> Ok
>>>>>> -ÂÂÂ clk_disable_unprepare(data->clk_cdev1);
>>>>>> -ÂÂÂ clk_disable_unprepare(data->clk_pll_a_out0);
>>>>>> -ÂÂÂ clk_disable_unprepare(data->clk_pll_a);
>>>>>> +ÂÂÂ if (__clk_is_enabled(data->clk_cdev1))
>>>>>> +ÂÂÂÂÂÂÂ clk_disable_unprepare(data->clk_cdev1);
>>>>> The root of the problem is that you removed clocks enabling from
>>>>> tegra_asoc_utils_init().
>> currently, audio mclk and its parent clocks enabling are from clock
>> driver init and not from tegra_asoc_utils_init.
>>>>> I'm not sure why clocks should be disabled during the rate-changing,
>>>>> probably this action is not really needed.
>>>> I know nothing about this particular device but this is not that
>>>> unusual a restriction for audio hardware, you often can't
>>>> robustly reconfigure the clocking for a device while it's active
>>>> due to issues in the hardware. You often see issues with FIFOs
>>>> glitching or state machines getting stuck. This may not be an
>>>> issue here but if it's something that's documented as a
>>>> requirement it's probably good to pay attention.
>>> I don't know details about that hardware either, maybe it is simply not
>>> safe to change PLL_A rate dynamically and then CLK_SET_RATE_GATE could
>>> be used.
>>> If nobody knows for sure, then will be better to keep
>>> tegra_asoc_utils_set_rate() unchanged.
>> plla rate change through tegra_asoc_utils_set_rate() happens only when
>> there is not active playback or record corresponding to this sound
>> device.
>> So, I don't see reason for disabling clock during rate change and not
>> sure why we had this from the beginning.
>> Thierry/Sameer,
>> Can you please comment?
>> Yes, we can use CLK_SET_RATE_GATE for PLLA and remove clock disabling
>> before rate change.
> PLLA is used for both I2S controller clock and also for audio mclk. I2S
> driver suspend resume implementations takes care of enabling and
> disabling I2S clock but audio mclk will be enabled during that time and
> PLLA disable might not happen. So using CLK_SET_RATE_GATE prevents rate
> change to happen and as rate change happens only when there is no active
> audio record/playback, we can perform rate change without disable/enable
> during rate change.
> So probably below changes should be good.
> * remove asoc_utils_set_rate call from asoc_utils_init as set_rate
> happens during existing hw_params callback implementations in sound
> drivers and there is no need to do rate change during asoc_utils_init.
> * remove disable/enable clocks during rate change in asoc_utils_set_rate.
> * add startup and shutdown snd_soc_ops callbacks to do enable and
> disable audio mclk.

Sounds good, thanks. I'll be happy to review and test it.