Re: [PATCH] PCI: Add CRS timeout for pci_device_is_present()

[Bjorn Helgaas <helgaas@kernel.org>]

On Wed, Nov 13, 2019 at 12:20:43PM +0100, Thierry Reding wrote:
> On Tue, Nov 12, 2019 at 12:58:44PM -0600, Bjorn Helgaas wrote:

> > My question is whether this wait should be connected somehow with
> > platform_pci_set_power_state().  It sounds like the tegra host
> > controller driver already does the platform-specific delays, and I'm
> > not sure it's reasonable for platform_pci_set_power_state() to do the
> > CRS polling.  Maybe something like this?  I'd really like to get
> > Rafael's thinking here.
> > 
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index e7982af9a5d8..052fa316c917 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -964,9 +964,14 @@ void pci_refresh_power_state(struct pci_dev *dev)
> >   */
> >  void pci_power_up(struct pci_dev *dev)
> >  {
> > +	pci_power_state_t prev_state = dev->current_state;
> > +
> >  	if (platform_pci_power_manageable(dev))
> >  		platform_pci_set_power_state(dev, PCI_D0);
> >  
> > +	if (prev_state == PCI_D3cold)
> > +		pci_dev_wait(dev, "D3cold->D0", PCIE_RESET_READY_POLL_MS);
> 
> Is there any reason in particular why you chose to call pci_dev_wait()?
> It seems to me like that's a little broader than pci_bus_wait_crs(). The
> latter is static in drivers/pci/probe.c so we'd need to change that in
> order to use it from drivers/pci/pci.c, but it sounds like the more
> explicit thing to do.

Broader in what sense?  They work essentially identically except that
pci_bus_wait_crs() doesn't need a pci_dev * (because it's used during
enumeration when we don't have a pci_dev yet) and it does dword reads
instead of word reads.

It is a shame that the logic is duplicated, but we don't have to worry
about that here.

I think I would stick with pci_dev_wait() in this case since we do
have a pci_dev * and it's a little simpler, unless I'm missing the
advantage of pci_bus_wait_crs().

Bjorn