PCI: MSI: Restore read_msi_msg_desc(); add get_cached_msi_msg_desc()

commit 2ca1af9aa3285c6a5f103ed31ad09f7399fc65d7 "PCI: MSI: Remove
unsafe and unnecessary hardware access" changed read_msi_msg_desc() to
return the last MSI message written instead of reading it from the
device, since it may be called while the device is in a reduced
power state.

However, the pSeries platform code really does need to read messages
from the device, since they are initially written by firmware.
Therefore:
- Restore the previous behaviour of read_msi_msg_desc()
- Add new functions get_cached_msi_msg{,_desc}() which return the
  last MSI message written
- Use the new functions where appropriate
Acked-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

arch/ia64/kernel/msi_ia64.c

@@ -25,7 +25,7 @@ static int ia64_set_msi_irq_affinity(unsigned int irq,
 	if (irq_prepare_move(irq, cpu))
 		return -1;
 
-	read_msi_msg(irq, &msg);
+	get_cached_msi_msg(irq, &msg);
 
 	addr = msg.address_lo;
 	addr &= MSI_ADDR_DEST_ID_MASK;

arch/ia64/sn/kernel/msi_sn.c

@@ -175,7 +175,7 @@ static int sn_set_msi_irq_affinity(unsigned int irq,
 	 * Release XIO resources for the old MSI PCI address
 	 */
 
-	read_msi_msg(irq, &msg);
+	get_cached_msi_msg(irq, &msg);
         sn_pdev = (struct pcidev_info *)sn_irq_info->irq_pciioinfo;
 	pdev = sn_pdev->pdi_linux_pcidev;
 	provider = SN_PCIDEV_BUSPROVIDER(pdev);

arch/x86/kernel/apic/io_apic.c

@@ -3397,7 +3397,7 @@ static int set_msi_irq_affinity(unsigned int irq, const struct cpumask *mask)
 
 	cfg = desc->chip_data;
 
-	read_msi_msg_desc(desc, &msg);
+	get_cached_msi_msg_desc(desc, &msg);
 
 	msg.data &= ~MSI_DATA_VECTOR_MASK;
 	msg.data |= MSI_DATA_VECTOR(cfg->vector);

drivers/pci/msi.c

@@ -197,9 +197,46 @@ void read_msi_msg_desc(struct irq_desc *desc, struct msi_msg *msg)
 {
 	struct msi_desc *entry = get_irq_desc_msi(desc);
 
-	/* We do not touch the hardware (which may not even be
-	 * accessible at the moment) but return the last message
-	 * written.  Assert that this is valid, assuming that
+	BUG_ON(entry->dev->current_state != PCI_D0);
+
+	if (entry->msi_attrib.is_msix) {
+		void __iomem *base = entry->mask_base +
+			entry->msi_attrib.entry_nr * PCI_MSIX_ENTRY_SIZE;
+
+		msg->address_lo = readl(base + PCI_MSIX_ENTRY_LOWER_ADDR);
+		msg->address_hi = readl(base + PCI_MSIX_ENTRY_UPPER_ADDR);
+		msg->data = readl(base + PCI_MSIX_ENTRY_DATA);
+	} else {
+		struct pci_dev *dev = entry->dev;
+		int pos = entry->msi_attrib.pos;
+		u16 data;
+
+		pci_read_config_dword(dev, msi_lower_address_reg(pos),
+					&msg->address_lo);
+		if (entry->msi_attrib.is_64) {
+			pci_read_config_dword(dev, msi_upper_address_reg(pos),
+						&msg->address_hi);
+			pci_read_config_word(dev, msi_data_reg(pos, 1), &data);
+		} else {
+			msg->address_hi = 0;
+			pci_read_config_word(dev, msi_data_reg(pos, 0), &data);
+		}
+		msg->data = data;
+	}
+}
+
+void read_msi_msg(unsigned int irq, struct msi_msg *msg)
+{
+	struct irq_desc *desc = irq_to_desc(irq);
+
+	read_msi_msg_desc(desc, msg);
+}
+
+void get_cached_msi_msg_desc(struct irq_desc *desc, struct msi_msg *msg)
+{
+	struct msi_desc *entry = get_irq_desc_msi(desc);
+
+	/* Assert that the cache is valid, assuming that
 	 * valid messages are not all-zeroes. */
 	BUG_ON(!(entry->msg.address_hi | entry->msg.address_lo |
 		 entry->msg.data));
@@ -207,11 +244,11 @@ void read_msi_msg_desc(struct irq_desc *desc, struct msi_msg *msg)
 	*msg = entry->msg;
 }
 
-void read_msi_msg(unsigned int irq, struct msi_msg *msg)
+void get_cached_msi_msg(unsigned int irq, struct msi_msg *msg)
 {
 	struct irq_desc *desc = irq_to_desc(irq);
 
-	read_msi_msg_desc(desc, msg);
+	get_cached_msi_msg_desc(desc, msg);
 }
 
 void write_msi_msg_desc(struct irq_desc *desc, struct msi_msg *msg)

include/linux/msi.h

@@ -14,8 +14,10 @@ struct irq_desc;
 extern void mask_msi_irq(unsigned int irq);
 extern void unmask_msi_irq(unsigned int irq);
 extern void read_msi_msg_desc(struct irq_desc *desc, struct msi_msg *msg);
+extern void get_cached_msi_msg_desc(struct irq_desc *desc, struct msi_msg *msg);
 extern void write_msi_msg_desc(struct irq_desc *desc, struct msi_msg *msg);
 extern void read_msi_msg(unsigned int irq, struct msi_msg *msg);
+extern void get_cached_msi_msg(unsigned int irq, struct msi_msg *msg);
 extern void write_msi_msg(unsigned int irq, struct msi_msg *msg);
 
 struct msi_desc {