linux-kernel - Re: [PATCH] ASoC: SOF: Intel: hda: unsolicited RIRB response

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Date:   Thu, 11 Jun 2020 15:36:58 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Takashi Iwai <tiwai@...e.de>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>
Cc:     "Lu, Brent" <brent.lu@...el.com>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "authored:2/16=12%,added_lines:21/248=8%,removed_lines:5/84=6%,),Liam"
         Girdwood DRIVERS ")" <lgirdwood@...il.com>,
        "commit_signer:6/16=38%,authored:6/16=38%,added_lines:123/248=50% 
        ,removed_lines:36/84=43%,Kai" Vehmanen DRIVERS ")" 
        <kai.vehmanen@...ux.intel.com>,
        "Daniel Baluta DRIVERS )" <daniel.baluta@....com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        "Rojewski, Cezary" <cezary.rojewski@...el.com>,
        Zhu Yingjiang <yingjiang.zhu@...ux.intel.com>,
        Keyon Jie <yang.jie@...ux.intel.com>,
        Bard Liao <yung-chuan.liao@...ux.intel.com>,
        "sound-open-firmware@...a-project.orgDRIVERS" 
        <sound-open-firmware@...a-project.orgDRIVERS>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ASoC: SOF: Intel: hda: unsolicited RIRB response


>>>> I added debug messages to print the RIRBWP register and realize
>>>> that
>>>> response could come between the read of RIRBWP in the
>>>> snd_hdac_bus_update_rirb() function and the interrupt clear in the
>>>> hda_dsp_stream_interrupt() function. The response is not handled
>>>> but
>>>> the interrupt is already cleared. It will cause timeout unless more
>>>> responses coming to RIRB.
>>>
>>> Now I noticed that the legacy driver already addressed it recently
>>> via
>>> commit 6d011d5057ff
>>>      ALSA: hda: Clear RIRB status before reading WP
>>>
>>> We should have checked SOF at the same time, too...
>>
>> Thanks, Takashi. But the legacy driver but doesnt remove the loop. The
>> loop added in the SOF driver was based on the legacy driver and
>> specifically to handle missed stream interrupts. Is there any harm in
>> keeping the loop?
> 
> A loop there might be safer to keep, indeed.  That's basically for a
> difference kind of race, and it can still happen theoretically.
> 
> Though, SOF is with the threaded interrupt, and it's interesting how
> the behavior differs.  I can imagine that, if a thread irq is running
> while a new IRQ is re-triggered, the hard irq handler won't queue it
> again.  But I might be wrong here, need some checks.

IIRC we added this loop before merging all interrupt handling in one 
thread, somehow the MSI mode never worked reliably without this change, 
so maybe we don't need this loop any longer.

I'd really prefer it if we didn't tie the RIRB handing change to this 
loop change, removing the loop should only be done with *a lot of testing*.