On Fri, Oct 25, 2019 at 02:23:18AM +0800, Tzung-Bi Shih wrote:

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.

Wow, that's a bit special. I'm wondering if the PLL unlock error handling isn't connected to the PLL configuration?

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.

Sleeping after starting a PLL to give it time to lock is pretty normal. Doing so after stopping is a bit more fun.

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.

I think so.

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."

That does sound like it might be causing problems, yes - even if it's not the problem you're seeing it's probably a good idea to try to follow the datsheet recommendation in case it's causing some other problem.

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.

No idea from me on any of that. Upstream the sleep between shutdown and on was added in the original code to do the recovery from Jarkko, b8a3ee820f7b0 (ASoC: max98090: Add recovery for PLL lock failure) - the ChromeOS patch you linked to claims to be a backport but clearly isn't a backport from upstream. It's missing the first sleep, the second sleep is shorter but it polls for success instead of just dead reckoning and not reading back. The "upstream" commit that the ChromeOS commit references just doesn't exist upstream so no idea what they were backporting from.

If the ChromeOS code is working for you we may as well get it upstream, if we can start the PLL faster than the 10ms that's a win and the confirmation that we got lock looks like a win too.

Hi

On 10/24/19 9:23 PM, Tzung-Bi Shih wrote:

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.

My memory is vague but one thing came to my mind - is codec I2S master or slave in your setup? I think we were using codec in slave mode only. However don't know does PLL unlock issue occurs when codec is master.

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.

No ULK interrupt is disabled until max98090_pll_det_enable_work() enables it 10 ms after stream start.

If I remember correctly we were getting quite often or always PLL unlock interrupts shortly after stream start even PLL locked itself successfully. On those cases workaround was kind of needless and probably caused pop noise or similar.

So idea was to activate PLL unlock detection after 10 ms and do the workaround only if interrupt happens after that 10 ms "do not detect" period. Liam please correct if I remember wrong.

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.

Yeah, that's looks like the one of the Liam's original workarounds for the issue. In that case looping 10 times. We were experimenting a lot around the issue and the commit b8a3ee820f7b ("ASoC: max98090: Add recovery for PLL lock failure") is the one combining our efforts together in the single commit.

Don't remember what incarnation brought these 10 ms sleeps between shutdown toggling and after. I'm guessing one for making sure codec reaches the shutdown and another perhaps for limiting that workaround is not run too soon again.