[PATCH 1/1] powerpc: Force 32 bit MSIs on systems lacking firmware support

[Brian King]

Recent commit e61133dda480062d221f09e4fc18f66763f8ecd0 added support
for a new firmware feature to force an adapter to use 32 bit MSIs.
However, this firmware is not available for all systems. The hack below
allows devices needing 32 bit MSIs to work on these systems as well.
It is careful to only enable this on Gen2 slots, which should limit
this to configurations where this hack is needed and tested to work.

Signed-off-by: Brian King <brking at linux.vnet.ibm.com>
---

 arch/powerpc/platforms/pseries/msi.c |   31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

diff -puN arch/powerpc/platforms/pseries/msi.c~powerpc_32bit_msi_hack_on_papr arch/powerpc/platforms/pseries/msi.c
--- linux/arch/powerpc/platforms/pseries/msi.c~powerpc_32bit_msi_hack_on_papr	2013-05-15 10:44:46.000000000 -0500
+++ linux-bjking1/arch/powerpc/platforms/pseries/msi.c	2013-05-20 15:24:52.000000000 -0500
@@ -397,10 +397,11 @@ static int check_msix_entries(struct pci
 static int rtas_setup_msi_irqs(struct pci_dev *pdev, int nvec_in, int type)
 {
 	struct pci_dn *pdn;
-	int hwirq, virq, i, rc;
+	int hwirq, virq, i, rc = -1;
 	struct msi_desc *entry;
 	struct msi_msg msg;
 	int nvec = nvec_in;
+	int use_32bit_msi_hack = 0;
 
 	pdn = get_pdn(pdev);
 	if (!pdn)
@@ -428,15 +429,37 @@ static int rtas_setup_msi_irqs(struct pc
 	 */
 again:
 	if (type == PCI_CAP_ID_MSI) {
-		if (pdn->force_32bit_msi)
+		if (pdn->force_32bit_msi) {
 			rc = rtas_change_msi(pdn, RTAS_CHANGE_32MSI_FN, nvec);
-		else
+			if (rc < 0) {
+				/* We only want to run the 32 bit MSI hack below if
+				 the max bus speed is Gen2 speed. */
+				if (pdev->bus->max_bus_speed != PCIE_SPEED_5_0GT)
+					return rc;
+
+				use_32bit_msi_hack = 1;
+			}
+		}
+
+		if (rc < 0)
 			rc = rtas_change_msi(pdn, RTAS_CHANGE_MSI_FN, nvec);
 
-		if (rc < 0 && !pdn->force_32bit_msi) {
+		if (rc < 0) {
 			pr_debug("rtas_msi: trying the old firmware call.\n");
 			rc = rtas_change_msi(pdn, RTAS_CHANGE_FN, nvec);
 		}
+
+		if (use_32bit_msi_hack && rc > 0) {
+			int pos;
+			u32 addr_hi, addr_lo;
+
+			dev_info(&pdev->dev, "rtas_msi: No 32 bit MSI firmware support, forcing 32 bit MSI\n");
+			pos = pci_find_capability(pdev, PCI_CAP_ID_MSI);
+			pci_read_config_dword(pdev, pos + PCI_MSI_ADDRESS_HI, &addr_hi);
+			addr_lo = 0xffff0000 | ((addr_hi >> (48 - 32)) << 4);
+			pci_write_config_dword(pdev, pos + PCI_MSI_ADDRESS_LO, addr_lo);
+			pci_write_config_dword(pdev, pos + PCI_MSI_ADDRESS_HI, 0);
+		}
 	} else
 		rc = rtas_change_msi(pdn, RTAS_CHANGE_MSIX_FN, nvec);
 
_