PCI MSI: Fix restoration of MSI/MSI-X mask states in suspend/resume

There are 2 problems on mask states in suspend/resume.

[1]:
It is better to restore the mask states of MSI/MSI-X to initial states
(MSI is unmasked, MSI-X is masked) when we release the device.
The pci_msi_shutdown() does the restoration of mask states for MSI,
while the msi_free_irqs() does it for MSI-X.  In other words, in the
"disable" path both of MSI and MSI-X are handled, but in the "shutdown"
path only MSI is handled.

MSI:
   pci_disable_msi()
      => pci_msi_shutdown()
         [ mask states for MSI restored ]
         => msi_set_enable(dev, pos, 0);
      => msi_free_irqs()

MSI-X:
   pci_disable_msix()
      => pci_msix_shutdown()
         => msix_set_enable(dev, 0);
      => msix_free_all_irqs
         => msi_free_irqs()
            [ mask states for MSI-X restored ]

This patch moves the masking for MSI-X from msi_free_irqs() to
pci_msix_shutdown().

This change has some positive side effects:
 - It prevents OS from touching mask states before reading preserved
   bits in the register, which can be happen if msi_free_irqs() is
   called from error path in msix_capability_init().
 - It also prevents touching the register after turning off MSI-X in
   "disable" path, which can be a problem on some devices.

[2]:
We have cache of the mask state in msi_desc, which is automatically
updated when msi/msix_mask_irq() is called.  This cached states are
used for the resume.

But since what need to be restored in the resume is the states before
the shutdown on the suspend, calling msi/msix_mask_irq() from
pci_msi/msix_shutdown() is not appropriate.

This patch introduces __msi/msix_mask_irq() that do mask as same
as msi/msix_mask_irq() but does not update cached state, for use
in pci_msi/msix_shutdown().

[updated: get rid of msi/msix_mask_irq_nocache() (proposed by Matthew Wilcox)]
Reviewed-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

drivers/pci/msi.c

@@ -127,17 +127,23 @@ static inline __attribute_const__ u32 msi_enabled_mask(u16 control)
  * reliably as devices without an INTx disable bit will then generate a
  * level IRQ which will never be cleared.
  */
-static void msi_mask_irq(struct msi_desc *desc, u32 mask, u32 flag)
+static u32 __msi_mask_irq(struct msi_desc *desc, u32 mask, u32 flag)
 {
 	u32 mask_bits = desc->masked;
 
 	if (!desc->msi_attrib.maskbit)
-		return;
+		return 0;
 
 	mask_bits &= ~mask;
 	mask_bits |= flag;
 	pci_write_config_dword(desc->dev, desc->mask_pos, mask_bits);
-	desc->masked = mask_bits;
+
+	return mask_bits;
+}
+
+static void msi_mask_irq(struct msi_desc *desc, u32 mask, u32 flag)
+{
+	desc->masked = __msi_mask_irq(desc, mask, flag);
 }
 
 /*
@@ -147,7 +153,7 @@ static void msi_mask_irq(struct msi_desc *desc, u32 mask, u32 flag)
  * file.  This saves a few milliseconds when initialising devices with lots
  * of MSI-X interrupts.
  */
-static void msix_mask_irq(struct msi_desc *desc, u32 flag)
+static u32 __msix_mask_irq(struct msi_desc *desc, u32 flag)
 {
 	u32 mask_bits = desc->masked;
 	unsigned offset = desc->msi_attrib.entry_nr * PCI_MSIX_ENTRY_SIZE +
@@ -155,7 +161,13 @@ static void msix_mask_irq(struct msi_desc *desc, u32 flag)
 	mask_bits &= ~1;
 	mask_bits |= flag;
 	writel(mask_bits, desc->mask_base + offset);
-	desc->masked = mask_bits;
+
+	return mask_bits;
+}
+
+static void msix_mask_irq(struct msi_desc *desc, u32 flag)
+{
+	desc->masked = __msix_mask_irq(desc, flag);
 }
 
 static void msi_set_mask_bit(unsigned irq, u32 flag)
@@ -616,9 +628,11 @@ void pci_msi_shutdown(struct pci_dev *dev)
 	pci_intx_for_msi(dev, 1);
 	dev->msi_enabled = 0;
 
+	/* Return the device with MSI unmasked as initial states */
 	pci_read_config_word(dev, pos + PCI_MSI_FLAGS, &ctrl);
 	mask = msi_capable_mask(ctrl);
-	msi_mask_irq(desc, mask, ~mask);
+	/* Keep cached state to be restored */
+	__msi_mask_irq(desc, mask, ~mask);
 
 	/* Restore dev->irq to its default pin-assertion irq */
 	dev->irq = desc->msi_attrib.default_irq;
@@ -658,7 +672,6 @@ static int msi_free_irqs(struct pci_dev* dev)
 
 	list_for_each_entry_safe(entry, tmp, &dev->msi_list, list) {
 		if (entry->msi_attrib.is_msix) {
-			msix_mask_irq(entry, 1);
 			if (list_is_last(&entry->list, &dev->msi_list))
 				iounmap(entry->mask_base);
 		}
@@ -746,9 +759,17 @@ static void msix_free_all_irqs(struct pci_dev *dev)
 
 void pci_msix_shutdown(struct pci_dev* dev)
 {
+	struct msi_desc *entry;
+
 	if (!pci_msi_enable || !dev || !dev->msix_enabled)
 		return;
 
+	/* Return the device with MSI-X masked as initial states */
+	list_for_each_entry(entry, &dev->msi_list, list) {
+		/* Keep cached states to be restored */
+		__msix_mask_irq(entry, 1);
+	}
+
 	msix_set_enable(dev, 0);
 	pci_intx_for_msi(dev, 1);
 	dev->msix_enabled = 0;