Re: [PATCH v7 1/5] PCI: qcom: Add system suspend and resume support

[Bjorn Helgaas]

[+cc Marc, Kevin]

On Wed, Oct 12, 2022 at 07:36:52PM +0530, Krishna Chaitanya Chundru wrote:
> On 10/6/2022 2:43 AM, Bjorn Helgaas wrote:

[I'm declaring quote text bankruptcy and dropping the huge wall of
text.  The IRQ affinity change you mention seems to be the critical
issue :)]

> > The PCIe spec clearly envisions Refclk being turned off
> > (sec 5.5.3.3.1) and PHYs being powered off (sec 5.5.3.2) while in
> > L1.2.
> > 
> > I've been assuming L1.2 exit (which includes Refclk being turned on
> > and PHYs being powered up) is completely handled by hardware, but it
> > sounds like the Qcom controller needs software assistance which fields
> > an interrupt when CLKREQ# is asserted and turns on Refclk and the
> > PHYs?
> > 
> > 5.5.3 does say "All Link and PHY state must be maintained during L1.2,
> > or must be restored upon exit using implementation specific means",
> > and maybe Qcom counts as using implementation specific means.
> > 
> > I *am* concerned about whether software can do the L1.2 exit fast
> > enough, but the biggest reason I'm struggling with this is because
> > using the syscore framework to work around IRQ affinity changes that
> > happen late in suspend just seems kind of kludgy and it doesn't seem
> > like it fits cleanly in the power management model.
> 
> Can you please suggest any another way to work around IRQ affinity
> changes.

One of your earlier patches [1] made dw_msi_mask_irq() look like this:

  static void dw_msi_mask_irq(struct irq_data *d)
  {
    struct pcie_port *pp = irq_data_get_irq_chip_data(d->parent_data);
    struct dw_pcie *pci = to_dw_pcie_from_pp(pp);

    if (dw_pcie_link_up(pci))
	    pci_msi_mask_irq(d);

    irq_chip_mask_parent(d);
  }

That was an awful lot like Marc's suggestion [2] that the
pci_msi_mask_irq() should be redundant.

If it's truly redundant, maybe pci_msi_mask_irq() can be removed
from dw_msi_mask_irq() (and other similar *_mask_irq()
implementations) completely?

Bjorn

[1] https://lore.kernel.org/r/1659526134-22978-3-git-send-email-quic_krichai@xxxxxxxxxxx
[2] https://lore.kernel.org/linux-pci/86k05m7dkr.wl-maz@xxxxxxxxxx/