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

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Message-ID: <defa5f61-c4f2-aeb6-da23-a39539ec64fc@linux.intel.com>
Date:   Tue, 12 Sep 2023 10:02:04 -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 9/12/23 02:10, Péter Ujfalusi wrote:
> 
> 
> On 12/09/2023 03:25, Pierre-Louis Bossart wrote:
>>
>>
>>> What we have atm:
>>> snd_sof_probe - might be called from wq
>>> snd_sof_remove - might be called from wq (cleans up the snd_sof_probe
>>> 		 step)
>>
>> I don't think it's correct, snd_sof_remove cannot be called from a wq.
>> The device core knows nothing about workqueues.
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/sound/soc/sof/core.c#n328
> 
> it is called on the error path of sof_probe_continue(), which can be run
> in a workque.
> 
>>> We want a callbacks for hardware/device probing, right, split the
>>> snd_sof_probe (and remove) to be able to support a sane level of
>>> deferred probing support.
>>>
>>> With that in mind:
>>> snd_sof_device_probe - Not called from wq (to handle deferred probing)
>>> snd_sof_probe - might be called from wq
>>>
>>> snd_sof_remove - might be called from wq (cleans up the snd_sof_probe
>>> 		 step)
>>> snd_sof_device_remove - Not called from wq (to up the
>>> 			snd_sof_device_probe step)
>>>
>>> Naming option: s/device/hardware
>>
>> I like the 'device' hint since it's directly related to the device (or
>> subsystem) callbacks.
>>
>>> However, I think the snd_sof_device_remove itself is redundant and we
>>> might not need it at all as in case we have wq and there is a failure in
>>> there we do want to release resources as much as possible. The module
>>> will be kept loaded (no deferred handling in wq) and that might block
>>> PM, other devices to behave correctly. Iow, if the wq has failure we
>>> should do a cleanup to the best effort to reach a level like the driver
>>> is not even loaded.
>>
>> If we have a failure in a workqueue used for probe, then we have to
>> clean-up everything since nothing in the device core will do so for us.
> 
> Yes, this makes the snd_sof_device_remove() redundant or at least the
> definition of it is no longer a mirror of snd_sof_device_probe():
> 
> snd_sof_device_remove - might be called from wq (cleans up the
> 			snd_sof_device_probe step)
> 
> Any failure in sof_probe_continue() should execute the
> snd_sof_device_remove(), snd_sof_remove() is only involved after the
> snd_sof_probe() have returned with success.
> 
> I think this makes actually makes sense and it is well defined.
> On module remove we need to take into account the case when we have
> failed in wq similarly as we do currently (the resources have been freed
> up already).

Agree, I stand corrected, thanks Peter.