Hi,
I am studying an odd issue of max98090 codec on Baytrail-based chromebook. The issue is: when user playback and capture simultaneously, it seems the PLL never get locked if msleep(10) between the SHDN off and on (https://elixir.bootlin.com/linux/v5.4-rc2/source/sound/soc/codecs/max98090.c...). The playback stream becomes silent and the console keeps printing "PLL unlocked". But, if comment out the msleep(10) between the SHDN off and on, the issue fixed. I am trying to find the reason but facing further more questions and may need your inputs.
1. The commit b8a3ee820f7b ("ASoC: max98090: Add recovery for PLL lock failure") enables ULK interrupts (https://elixir.bootlin.com/linux/v5.4-rc2/source/sound/soc/codecs/max98090.c...) when PCM stream starting. If max98090 claims its PLL is unlocked, max98090_pll_work() get scheduled to workaround it by SHDN off and on (https://elixir.bootlin.com/linux/v5.4-rc2/source/sound/soc/codecs/max98090.c...).
I feel it is weird to sleep in max98090_pll_work(). Especially, at this line https://elixir.bootlin.com/linux/v5.4-rc2/source/sound/soc/codecs/max98090.c... (it makes less sense to "wait" in another thread). Note that, the threaded IRQF_ONESHOT handler and max98090_pll_work() are in 2 different threads.
I guess the original intention is: - disable ULK interrupt in IRQ handler (https://elixir.bootlin.com/linux/v5.4-rc2/source/sound/soc/codecs/max98090.c...) - schedule max98090_pll_work() to workaround it - wait 10ms to give PLL chance to lock - enable ULK interrupt again If max98090 claims its PLL is unlocked again, repeat the above by receiving another ULK interrupt.
Unfortunately, the odd issue seems not be fixed by my rough implementation of these.
2. According to the datasheet page 164 table 90 (https://datasheets.maximintegrated.com/en/ds/MAX98090.pdf), there are some registers should only be adjusted when SHDN==0. But I fail to find max98090.c tries to set SHDN to 0 and restore it afterwards when writing to these registers. For example, https://elixir.bootlin.com/linux/v5.4-rc2/source/sound/soc/codecs/max98090.c.... I am wondering if it would bring any side effects because the datasheet states "Changing these settings during normal operation (SHDN=1) can compromise device stability and performance specifications."
3. By searching some history data, I found a previous version did not have the msleep(10) between the SHDN off and on (https://crrev.com/c/191740, click the file name in the middle of the window to see the diff. Pardon me, I do not find another public repository for this). I am curious if anyone of you still remember why the upstream version contains the msleep(10). I am also curious if anyone of your environment works well with the upstream version max98090.c.