Re: [PATCH RESEND] PCI: disable runtime PM for PLX switches

[Bjorn Helgaas <helgaas@kernel.org>]

On Wed, Apr 24, 2019 at 05:58:19PM +0300, Mika Westerberg wrote:
> On Wed, Apr 24, 2019 at 09:11:48AM -0500, Bjorn Helgaas wrote:
> >   - Maybe the PCI sysfs accessors (pci_mmap_resource(), etc) should
> >     turn off runtime PM?  If we allow mmap of a BAR and then put the
> >     device in D3hot, that seems like a bug that could affect lots of
> >     things.  But maybe that's already done magically elsewhere?
> 
> IIRC there is no PM magic happening for MMIO userspace accesses.
> 
> What you suggest above sounds like a good way to fix it. We already do
> similar for config space access from userspace (if the device is in
> D3cold) so definitely makes sense to do the same for MMIO. However, I
> don't think we need to disable runtime PM - it should be enough to
> increase the reference count (pm_runtime_get_sync() and friends) during
> the time the MMIO resource is mmapped.

OK, so if I understand correctly this would be basically adding
pm_runtime_get_sync(dev) in pci_mmap_resource().  I don't know what
the unmap path is, but there would have to be a matching
pm_runtime_put() somewhere.

And a similar change in the read/write path for /sys/.../resource<N>;
I think this must be related to the sysfs_create_bin_file() call in
pci_create_attr(), but I don't see the path where the actual
read/write to the device is done.

And probably something similar should be done in pci_resource_io(),
pci_map_rom(), and pci_unmap_rom().

Bjorn