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

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Date:   Fri, 27 Dec 2019 13:19:59 -0800
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Dmitry Osipenko <digetx@...il.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


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.