Messages in this thread | | | Date | Mon, 23 Jan 2023 15:51:58 +0000 | Subject | Re: [PATCH v2 6/8] ASoC: cs42l42: Add Soundwire support | From | Richard Fitzgerald <> |
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On 20/01/2023 19:55, Pierre-Louis Bossart wrote: > > > On 1/19/23 09:35, Richard Fitzgerald wrote: >> On 19/1/23 14:48, Pierre-Louis Bossart wrote: >>> >>>>>> +static int cs42l42_sdw_dai_startup(struct snd_pcm_substream >>>>>> *substream, >>>>>> + struct snd_soc_dai *dai) >>>>>> +{ >>>>>> + struct cs42l42_private *cs42l42 = >>>>>> snd_soc_component_get_drvdata(dai->component); >>>>>> + >>>>>> + if (!cs42l42->init_done) >>>>>> + return -ENODEV; >>>>> >>>>> Can this happen? IIRC the ASoC framework would use >>>>> pm_runtime_resume_and_get() before .startup, which would guarantee that >>>>> the device is initialized, no? >>>>> >>>> >>>> Yes, this can happen. Because of the way that the SoundWire enumeration >>>> was implemented in the core code, it isn't a probe event so we cannot >>>> call snd_soc_register_component() on enumeration because -EPROBE_DEFER >>>> wouldn't be handled. So the snd_soc_register_component() must be called >>>> from probe(). This leaves a limbo situation where we've registered the >>>> driver but in fact don't yet have any hardware. ALSA/ASoC doesn't know >>>> that we've registered before we are functional so they are happy to >>>> go ahead and try to use the soundcard. If for some reason the hardware >>>> failed to enumerate we can get here without having enumerated. >>> >>> Humm, yes, but you've also made the regmap cache-only, so is there >>> really a problem? >>> >> >> It's true that normally we go past these stages in cache-only, but that >> is because normally (non-Soundwire) we already initialized the hardware >> to good state during probe(). >> If we just carry on when it hasn't enumerated and we haven't initialized >> it yet, who knows what will happen if it enumerates some time later. >> >> We could just ignore it and see if anyone has a problem but for the sake >> of a couple of lines of code I feel like I'd rather check for it. >> >>> FWIW I don't see a startup callback in any other codec driver. It may be >>> wrong but it's also a sign that this isn't a problem we've seen so far >>> on existing Intel-based platforms. >>> >> >> It's nicer to do the check in startup() because then the application >> open() will fail cleanly. We could delay until prepare - which is the >> point we really need the hardware to be accessible - and hope the >> hardware enumerated and initialized by that time. But that's not so >> nice from the app point of view. > > Another way to avoid problems is to rely on the codec component .probe > to check if the SoundWire device is initialized before registering a card. > > I just tried with a system where the ACPI info exposes a codec which is > not connected, it fails nicely. That avoids the pitfalls of creating a > card which isn't functional since all dependencies are not met. > > [ 64.616530] snd_soc_sof_sdw:mc_probe: sof_sdw sof_sdw: Entry > [ 64.616549] snd_soc_sof_sdw:log_quirks: sof_sdw sof_sdw: quirk > SOF_SDW_PCH_DMIC enabled > [ 64.616559] snd_soc_sof_sdw:sof_card_dai_links_create: sof_sdw > sof_sdw: sdw 2, ssp 0, dmic 2, hdmi 0 > [ 64.616587] snd_soc_sof_sdw:init_dai_link: sof_sdw sof_sdw: create > dai link SDW0-Playback, id 0 > [ 64.616600] snd_soc_sof_sdw:init_dai_link: sof_sdw sof_sdw: create > dai link SDW0-Capture, id 1 > [ 64.616607] snd_soc_sof_sdw:init_dai_link: sof_sdw sof_sdw: create > dai link dmic01, id 2 > [ 64.616614] snd_soc_sof_sdw:init_dai_link: sof_sdw sof_sdw: create > dai link dmic16k, id 3 > [ 69.757115] rt5682 sdw:0:025d:5682:00: Initialization not complete, > timed out > [ 69.757128] rt5682 sdw:0:025d:5682:00: ASoC: error at > snd_soc_component_probe on sdw:0:025d:5682:00: -110 > [ 69.757224] sof_sdw sof_sdw: ASoC: failed to instantiate card -110 > [ 69.757734] sof_sdw sof_sdw: snd_soc_register_card failed -110 > > see > https://elixir.bootlin.com/linux/latest/source/sound/soc/codecs/rt5682.c#L2927 > > I think this is compatible with the device model and bind/unbind, but it > could be improved with the removal of the wait if we had a way to return > -EPROBEDEFER, and have a mechanism to force the deferred probe work to > be triggered when a device actually shows up. It's a generic problem > that the probe cannot always be a synchronous function but may complete > 'later'.
I see what you've done in your patch, but I had already experimented with this idea and found that the wait_for_completion() can deadlock the Soundwire core.
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