linux-kernel - Re: [PATCH v4 01/11] ASoC: SOF: core: add 'no

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Date:   Thu, 7 Sep 2023 13:29:49 -0400
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Péter Ujfalusi <peter.ujfalusi@...ux.intel.com>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Cc:     alsa-devel@...a-project.org, Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Cezary Rojewski <cezary.rojewski@...el.com>,
        Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
        Bard Liao <yung-chuan.liao@...ux.intel.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Mark Brown <broonie@...nel.org>,
        Daniel Baluta <daniel.baluta@....com>,
        linux-kernel@...r.kernel.org, sound-open-firmware@...a-project.org
Subject: Re: [PATCH v4 01/11] ASoC: SOF: core: add 'no_wq' probe and remove
 callbacks



On 9/5/23 08:37, Pierre-Louis Bossart wrote:
> 
> 
> On 9/1/23 08:44, Péter Ujfalusi wrote:
>>
>>
>> On 01/09/2023 15:15, Kai Vehmanen wrote:
>>> Hi,
>>>
>>> On Wed, 30 Aug 2023, Maarten Lankhorst wrote:
>>>
>>>> With the upcoming changes for i915/Xe driver relying on the
>>>> -EPROBE_DEFER mechanism, we need to have a first pass of the probe
>>>> which cannot be pushed to a workqueue. Introduce 2 new optional
>>>> callbacks.
>>> [...]
>>>> diff --git a/sound/soc/sof/core.c b/sound/soc/sof/core.c
>>>> index 30db685cc5f4b..54c384a5d6140 100644
>>>> --- a/sound/soc/sof/core.c
>>>> +++ b/sound/soc/sof/core.c
>>>> @@ -327,8 +327,6 @@ static int sof_probe_continue(struct snd_sof_dev *sdev)
>>>>  dsp_err:
>>>>  	snd_sof_remove(sdev);
>>>>  probe_err:
>>>> -	sof_ops_free(sdev);
>>>> -
>>>
>>> this seems a bit out-of-place in this patch. It seems a valid change,
>>> but not really related to this patch, right?
>>
>> The ops needs to be preserved even if the wq fails since the patch wants
>> to call snd_sof_remove_no_wq() unconditionally on remove.
>>
>>> We seem to have a related fix waiting to be sent to alsa-devel, by
>>> Peter:
>>> "ASoC: SOF: core: Only call sof_ops_free() on remove if the probe wa"
>>> https://github.com/thesofproject/linux/pull/4515
>>
>> I guess we can revert that in sof-dev, if this is the preferred way?
>>
>>> ... not yet in Mark's tree.
>>>
>>> Otherwise patch looks good to me.
>>
>> I would have not created the snd_sof_remove_no_wq() as it makes not much
>> functional sense.
>> It might be even better if the remove in the wq would do the
>> hda_codec_i915_exit() as the module will remain in there until the user
>> removes it.
> 
> I think find all this very confusing, because there is no workqueue used
> in the remove steps. The workqueue is only used ONCE during the probe.

Maybe we should just remove any references to workqueues, and have

probe_start (cannot run in a wq)
probe (may run in a wq)
remove (cannot run in a wq, needs to call cancel_work_sync() if the
probe runs in a wq)
remove_last (cannot run in a wq, releases all resources acquired in
probe_start)

Or something similar that shows the symmetry between steps and when the
wq is allowed.