linux-kernel - Re: [PATCH 1/3] ASoC: ti: omap-mcbsp: Ignore errors for getting fck

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Date:   Thu, 12 Oct 2023 17:41:34 +0300
From:   Péter Ujfalusi <peter.ujfalusi@...il.com>
To:     Andreas Kemnade <andreas@...nade.info>,
        Tony Lindgren <tony@...mide.com>
Cc:     bcousson@...libre.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        lgirdwood@...il.com, broonie@...nel.org, perex@...ex.cz,
        tiwai@...e.com, jarkko.nikula@...mer.com,
        dmitry.torokhov@...il.com, linux-omap@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        alsa-devel@...a-project.org
Subject: Re: [PATCH 1/3] ASoC: ti: omap-mcbsp: Ignore errors for getting
 fck_src

On 07/10/2023 10:11, Andreas Kemnade wrote:
>> OK good to hear it works, I'll send out fixes for omap4 and 5, seems
>> the runtime PM warning is something different.
>>
>>> omap-mcbsp 40124000.mcbsp: Runtime PM usage count underflow!
>>> # cat /sys/bus/platform/devices/40124000.mcbsp/power/runtime_status 
>>> active
>>>
>>> even with no sound.  
>>
> Well, it is a regression caused by your fix. Without it (and not reverting
> the already applied ignore patch), runtime is properly suspended. Don't know
> why yet.

I guess it is because of the pm_runtime_put_sync() in the
omap2_mcbsp_set_clks_src() around the fclk re-parenting.
That is a bit dubious thing for sure. We need to disable the device to
be able to re-parent the fclk but if we disable the device it is going
to be powered down, right? I think we have appropriate context handling,
so it might work, but it is certainly not a rock solid code... If you
have a stream running already, you don't really want to kill the McBSP.

The problem is that this mux is outside of the McBSP IP, so we need a
system level (iow, clk API) way to change it runtime.

What is the machine driver where this happens? If you set the sysclk in
hw_params of the machine driver, it will be OK, but if you do that in
probe time then it is likely going to fail as you experienced

-- 
Péter