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>

2 files changed, 2 insertions, 2 deletions

diff --git a/arch/ia64/kernel/msi_ia64.c b/arch/ia64/kernel/msi_ia64.c
index 6c8922856049..4a746ea838ff 100644
--- a/arch/ia64/kernel/msi_ia64.c
+++ b/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;
diff --git a/arch/ia64/sn/kernel/msi_sn.c b/arch/ia64/sn/kernel/msi_sn.c
index ebfdd6a9ae1a..0c72dd463831 100644
--- a/arch/ia64/sn/kernel/msi_sn.c
+++ b/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);