Pierre-Louis Bossart b450b87847 ASoC: core: don't increase component module refcount unconditionally ... The ASoC core has for the longest time increased the module reference counts, even before the transition to the component model. This is probably fine on most platforms, but it introduces a deadlock case on Intel devices with the Skylake and SOF drivers which cannot be removed due to their reference counts being modified by the core. In these 2 cases, the PCI or ACPI driver .probe creates a platform device to let the machine driver .probe register the audio card. Conversely the PCI or ACPI driver .remove will unregister the platform device which results in the card being removed by the machine driver .remove. With ascii art, this can be represented as modprobe snd_soc_skl/ soc-pci-dev/sof-acpci-dev ----------> pci/acpi probe ^ | | ---------------| | | | | V V increase register register machine refcount component platform_device ^ | | | | V component <---- register card <---- probe probe The issue is that by playing with the component's module reference counts during the card registration, it's no longer possible to remove the module which controls the component. This can be shown, e.g. with the following error: root@plb-XPS-13-9350:~# lsmod | grep snd_soc_skl snd_soc_skl 110592 1 root@plb-XPS-13-9350:~# rmmod snd_soc_skl rmmod: ERROR: Module snd_soc_skl is in use Increasing the reference count during the component probe is not useful. If the PCI/ACPI module is removed, the card will be removed anyway. To avoid breaking existing platforms and allowing Intel platforms to safely deal with module load/unload cases, this patch introduces a flag which needs to be set during the component initialization. This is a strictly opt-in capability that should only be used when the handling of the component module does not require a reference count increase to prevent removal during use. Note that this solution is not directly applicable to the legacy Atom/SST driver, which uses a different device hierarchy. There are however additional refcount issues which prevent the ACPI driver from being removed. This is a different issue which would need a different patch. Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com> Signed-off-by: Mark Brown <broonie@kernel.org>		2019-02-08 18:00:20 +00:00
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soc	ASoC: core: don't increase component module refcount unconditionally	2019-02-08 18:00:20 +00:00
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