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

Dmitry Osipenko
2019-12-27T14:56:20Z

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
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> 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.