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

[Alexander Fomichev <fomichev.ru@gmail.com>]

Hi.

On Wed, Apr 24, 2019 at 11:09:52PM +0200, Rafael J. Wysocki wrote:
> On Wed, Apr 24, 2019 at 8:01 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
> >
> > 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.
> 
> Right.
> 
> > 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().
> 
> In general, every path in which there is a memory or IO address space
> access requires pm_runtime_get_sync()/pm_runtime_put() around it as
> these accesses are only guaranteed to work in D0.
> 

Tested a solution based on proposals by Logan, Bjorn, Mika, Rafael (thanks all
of you, guys), I managed to fix the problem inside the PLX driver code. So no
additional quirks or other modifications in Linux kernel needed. I think
my patch can be easily rejected.

Thanks for help.

-- 
Regards,
  Alexander