Re: [alsa-devel] [PATCH v2 09/11] ASoC: Intel: hdac_hdmi: Set ops to NULL on remove

From: Pierre-Louis Bossart
Date: Thu Jun 20 2019 - 02:22:51 EST

Could you please give a bit more context on what error you see
when this happens?


I get Oops. This is what happens with all other patches in this
series and only this one reverted:

root@APL:~# rmmod snd_soc_sst_bxt_rt298
root@APL:~# rmmod snd_soc_hdac_hdmi
root@APL:~# rmmod snd_soc_skl

Thanks, Amadeusz. I think the order in which the drivers are
is what's causing the oops in your case. With SOF, the order we
remove is

1. rmmod sof_pci_dev
2. rmmod snd_soc_sst_bxt_rt298
3. rmmod snd_soc_hdac_hdmi

Well, there is nothing enforcing the order in which modules can be
unloaded (and I see no reason to force it), as you can see from
following excerpt, you can either start unloading from
snd_soc_sst_bxt_rt298 or snd_soc_skl, and yes if you start from
snd_soc_skl, there is no problem.

there is a fundamental dependency that you are ignoring: the module snd_soc_sst_bxt_rt298 is a machine driver which will be probed when snd_soc_skl creates a platform_device.
Sure you can remove modules in a different order, but that's a bit of an artificial/academic exercise isn't it?

I am good with this patch. I just wanted to understand why we werent
seeing this error with SOF. Sure, there's nothing enforcing the order
in which modules are unloaded but there must be a logical order for
testing purposes.

Pierre, can you please comment on it. I vaguely remember discussing
this with you last year.

Our tests remove the modules by taking care of dependencies and it's already unveiled dozens of issues.
We could add a sequence similar to Amadeusz and unbind the modules which are loaded with the creation of a platform_device (machine driver, dmic), I am just not sure how of useful this would be.