[PATCH] PCI:MSI Return -ENOSPC when requested vectors is not enough

[Dennis Chen]

The __pci_enable_msi_range() should return -ENOSPC instead of -EINVAL
when the device doesn't have enough vectors as required, just as the 
MSI-X vector allocator does in __pci_enable_msix_range(). Otherwise, 
some drivers depending on that return value will probably fallback to
the legacy interrupt directly, for example, in commit 17a51f12cfbd2814
("ahci: only try to use multi-MSI mode if there is more than 1 port"), the
ahci driver will fallback to single MSI mode only when the return value
is -ENOSPC in case of required vectors is not enough, else the driver will
use legacy interrupt which has been observed on a x86 box with 6-port SATA
controller.

With this patch, when a MSI-capable device doesn't have enough MSI
vectors as requested, it will fallback to single MSI mode while not
legacy interrupt.

Signed-off-by: Dennis Chen <dennis.chen at arm.com>
Cc: Tejun Heo <tj at kernel.org>
Cc: Christoph Hellwig <hch at lst.de>
Cc: Tom Long Nguyen <tom.l.nguyen at intel.com>
Cc: Bjorn Helgaas <bhelgaas at google.com>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: Marc Zyngier <marc.zyngier at arm.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
Cc: Steve Capper <steve.capper at arm.com>
Cc: linux-ide at vger.kernel.org
Cc: linux-arm-kernel at lists.infradead.org
---
 drivers/pci/msi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index ad70507..da37113 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -1084,7 +1084,7 @@ static int __pci_enable_msi_range(struct pci_dev *dev, int minvec, int maxvec,
 	if (nvec < 0)
 		return nvec;
 	if (nvec < minvec)
-		return -EINVAL;
+		return -ENOSPC;
 
 	if (nvec > maxvec)
 		nvec = maxvec;
-- 
2.7.4