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

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Date:   Thu, 2 Jan 2020 19:12:10 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sowjanya Komatineni <skomatineni@...dia.com>,
        Mark Brown <broonie@...nel.org>
Cc:     thierry.reding@...il.com, jonathanh@...dia.com,
        lgirdwood@...il.com, perex@...ex.cz, tiwai@...e.com,
        mperttunen@...dia.com, gregkh@...uxfoundation.org,
        sboyd@...nel.org, robh+dt@...nel.org, mark.rutland@....com,
        pdeschrijver@...dia.com, pgaikwad@...dia.com, spujar@...dia.com,
        josephl@...dia.com, daniel.lezcano@...aro.org,
        mmaddireddy@...dia.com, markz@...dia.com,
        devicetree@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 12/19] ASoC: tegra: Add initial parent configuration
 for audio mclk

02.01.2020 10:03, Sowjanya Komatineni пишет:
> 
> 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 пишет:
>>>> On Mon, Dec 23, 2019 at 12:14:34AM +0300, Dmitry Osipenko wrote:
>>>>> 21.12.2019 01:26, Sowjanya Komatineni пишет:
>>>>>> 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
>>>
>>>>>> -    clk_disable_unprepare(data->clk_cdev1);
>>>>>> -    clk_disable_unprepare(data->clk_pll_a_out0);
>>>>>> -    clk_disable_unprepare(data->clk_pll_a);
>>>>>> +    if (__clk_is_enabled(data->clk_cdev1))
>>>>>> +        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.