[PATCH 3.16 124/148] PCI/MSI: Fix incorrect MSI-X masking on resume

[Ben Hutchings]

3.16.82-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jian-Hong Pan <jian-hong@xxxxxxxxxxxx>

commit e045fa29e89383c717e308609edd19d2fd29e1be upstream.

When a driver enables MSI-X, msix_program_entries() reads the MSI-X Vector
Control register for each vector and saves it in desc->masked.  Each
register is 32 bits and bit 0 is the actual Mask bit.

When we restored these registers during resume, we previously set the Mask
bit if *any* bit in desc->masked was set instead of when the Mask bit
itself was set:

  pci_restore_state
    pci_restore_msi_state
      __pci_restore_msix_state
        for_each_pci_msi_entry
          msix_mask_irq(entry, entry->masked)   <-- entire u32 word
            __pci_msix_desc_mask_irq(desc, flag)
              mask_bits = desc->masked & ~PCI_MSIX_ENTRY_CTRL_MASKBIT
              if (flag)       <-- testing entire u32, not just bit 0
                mask_bits |= PCI_MSIX_ENTRY_CTRL_MASKBIT
              writel(mask_bits, desc_addr + PCI_MSIX_ENTRY_VECTOR_CTRL)

This means that after resume, MSI-X vectors were masked when they shouldn't
be, which leads to timeouts like this:

  nvme nvme0: I/O 978 QID 3 timeout, completion polled

On resume, set the Mask bit only when the saved Mask bit from suspend was
set.

This should remove the need for 19ea025e1d28 ("nvme: Add quirk for Kingston
NVME SSD running FW E8FK11.T").

[bhelgaas: commit log, move fix to __pci_msix_desc_mask_irq()]
Link: https://bugzilla.kernel.org/show_bug.cgi?id=204887
Link: https://lore.kernel.org/r/20191008034238.2503-1-jian-hong@xxxxxxxxxxxx
Fixes: f2440d9acbe8 ("PCI MSI: Refactor interrupt masking code")
Signed-off-by: Jian-Hong Pan <jian-hong@xxxxxxxxxxxx>
Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/pci/msi.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -220,8 +220,9 @@ u32 default_msix_mask_irq(struct msi_des
 	u32 mask_bits = desc->masked;
 	unsigned offset = desc->msi_attrib.entry_nr * PCI_MSIX_ENTRY_SIZE +
 						PCI_MSIX_ENTRY_VECTOR_CTRL;
+
 	mask_bits &= ~PCI_MSIX_ENTRY_CTRL_MASKBIT;
-	if (flag)
+	if (flag & PCI_MSIX_ENTRY_CTRL_MASKBIT)
 		mask_bits |= PCI_MSIX_ENTRY_CTRL_MASKBIT;
 	writel(mask_bits, desc->mask_base + offset);