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

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Message-ID: <20231013132503.25d63933@aktux>
Date:   Fri, 13 Oct 2023 13:25:03 +0200
From:   Andreas Kemnade <andreas@...nade.info>
To:     Péter Ujfalusi <peter.ujfalusi@...il.com>
Cc:     Tony Lindgren <tony@...mide.com>, 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 Thu, 12 Oct 2023 17:41:34 +0300
Péter Ujfalusi <peter.ujfalusi@...il.com> wrote:

> 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.
> 
Ok, so if the device is powered of at omap2_mcbsp_set_clks_src() 
we get the usage count underflow, and the counter is incremented
immediately again in the runtime put function. So things get out of balance...
I'll check Tony's fix here.

> 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
> 
As you see in the other patches of this series,
it is a simple-audio-card with a tlv320aic3x codec
in combination with the mcbsp.

Regards,
Andreas