[PATCH 2/2] powerpc/msi: clarify call to check_req_msi{,x}

[Nishanth Aravamudan]

The RTAS IRQ fixup code relies on a less-than-clear edge condition for
verifying a given device is not using MSI or MSI-X. Make that more clear
with a comment.

Signed-off-by: Nishanth Aravamudan <nacc at us.ibm.com>
Cc: Milton Miller <miltonm at bga.com>
Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Cc: Paul Mackerras <paulus at samba.org>

---
 arch/powerpc/platforms/pseries/msi.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/msi.c b/arch/powerpc/platforms/pseries/msi.c
index 9434576..8c6dbbc 100644
--- a/arch/powerpc/platforms/pseries/msi.c
+++ b/arch/powerpc/platforms/pseries/msi.c
@@ -455,7 +455,12 @@ static void rtas_msi_pci_irq_fixup(struct pci_dev *pdev)
 		return;
 	}
 
-	/* No MSI -> MSIs can't have been assigned by fw, leave LSI */
+	/* 
+	 * No MSI -> MSIs can't have been assigned by fw, leave LSI
+	 * The calls below can only provide one of two responses:
+	 *   < 0: if the device doesn't request MSI or MSI-X
+	 *   0: if the device requests at least 1 MSI/MSI-X vector
+	 */
 	if (check_req_msi(pdev, 1) && check_req_msix(pdev, 1)) {
 		dev_dbg(&pdev->dev, "rtas_msi: no req#msi/x, nothing to do.\n");
 		return;
-- 
1.7.1