[+cc George]
On Fri, Feb 23, 2018 at 10:51:47AM +0100, Lukas Wunner wrote:
On Tue, Feb 20, 2018 at 04:20:59PM -0600, Bjorn Helgaas wrote:
On Sun, Feb 18, 2018 at 09:38:32AM +0100, Lukas Wunner wrote:
The device link is added in a PCI quirk rather than in hda_intel.c. It is therefore legal for the GPU to runtime suspend to D3cold even if the HDA controller is not bound to a driver or if CONFIG_SND_HDA_INTEL is not enabled, for accesses to the HDA controller will cause the GPU to wake up regardless if they're occurring outside of hda_intel.c (think config space readout via sysfs).
I guess this GPU wakeup happens *if* the path accessing the HDA controller calls pm_runtime_get_sync() or similar, right?
Right.
We do have that in the sysfs config accessors via pci_config_pm_runtime_get(), but not in the sysfs mmap paths. I think that's a latent PCI core defect independent of this series.
Yes, there may be a few places where the parent of the device is erroneously not runtime resumed when sysfs files are accessed. I've never used the sysfs mmap feature, so never witnessed issues with it.
We also don't have that in PCI core config accessors. That maybe doesn't matter because the core probably shouldn't be touching devices after enumeration (although there might be holes there for things like ASPM where a sysfs file can cause reconfiguration of several devices).
I assume with PCI core config accessors you're referring to pci_read_config_word() and friends? Those are arguably hotpaths where we wouldn't want the overhead to check runtime PM status everytime. They might also be called from atomic context, I'm not sure, and the runtime PM callbacks may sleep by default (unless pm_runtime_irq_safe() was called).
Yes, I was thinking of pci_read_config_word(), etc. They're used by the core during enumeration and occasionally by drivers, and both cases already pay attention to PM. I think we have a few holes in the runtime sysfs area, but I think it's reasonable to deal with those in the callers.
So I don't think those need to actually *do* anything with PM status, although it might be interesting to add some (optional) checking there. George Cherian is turning up some issues in this area because he has a root port that reports errors with an exception instead of silently synthesizing all ones data like most hardware does [1].
Bjorn
[1] https://lkml.kernel.org/r/1517554846-16703-1-git-send-email-george.cherian@c...