On Thu, 27 Apr 2017 18:02:20 +0200, ville.syrjala@linux.intel.com wrote:
From: Ville Syrjälä ville.syrjala@linux.intel.com
Not calling pm_runtime_enable() means that runtime PM can't be enabled at all via sysfs. So we definitely need to call it from somewhere.
Calling it from the driver seems like a bad idea because it would have to be paired with a pm_runtime_disable() at driver unload time, otherwise the core gets upset. Also if there's no LPE audio driver loaded then we couldn't runtime suspend i915 either.
So it looks like a better plan is to call it from i915 when we register the platform device. That seems to match how pci generally does things. I cargo culted the pm_runtime_forbid() and pm_runtime_set_active() calls from pci as well.
The exposed runtime PM API is massive an thorougly misleading, so I don't actually know if this is how you're supposed to use the API or not. But it seems to work. I can now runtime suspend i915 again with or without the LPE audio driver loaded, and reloading the LPE audio driver also seems to work.
Note that powertop won't auto-tune runtime PM for platform devices, which is a little annoying. So I'm not sure that leaving runtime PM in "on" mode by default is the best choice here. But I've left it like that for now at least.
The reason I didn't proactively turn on the runtime PM was that it often caused a few seconds of pause to the A/V receivers before actually starting playing.
There is a planned feature to keep sending the silent stream even after stopping the stream, but it's not implemented yet.
Also remove the comment about there not being much benefit from LPE audio runtime PM. Not allowing runtime PM blocks i915 runtime PM, which will also block s0ix, and that could have a measurable impact on power consumption.
Cc: Takashi Iwai tiwai@suse.de Cc: Pierre-Louis Bossart pierre-louis.bossart@linux.intel.com Fixes: 0b6b524f3915 ("ALSA: x86: Don't enable runtime PM as default") Signed-off-by: Ville Syrjälä ville.syrjala@linux.intel.com
Reviewed-by: Takashi Iwai tiwai@suse.de
IMO, this should be tagged with Cc to stable.
thanks,
Takashi