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 17:56:06 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Sowjanya Komatineni <skomatineni@...dia.com>,
        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

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().
> 
>> 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.