Re: [PATCH] msi-x: let drivers retry when not enough vectors

On Thu, May 07, 2009 at 04:51:24PM +0800, Sheng Yang wrote:

On Thursday 07 May 2009 16:28:41 Michael S. Tsirkin wrote:

quoted

pci_enable_msix currently returns -EINVAL if you ask
for more vectors than supported by the device, which would
typically cause fallback to regular interrupts.

It's better to return the table size, making the driver retry
MSI-X with less vectors.

Hi Michael

I think driver should read from capability list to know how many vector 
supported by this device before enable MSI-X for device, as 
pci_msix_table_size() did...

Drivers can do this, but it's more code. Since pci_enable_msix
calls pci_msix_table_size already, let it do the work. Right?

-- 
regards
Yang, Sheng

quoted

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---

Hi Jesse,
This came up when I was adding MSI-X support to virtio pci driver,
which does not know the exact table size upfront.
Could you consider this patch for 2.6.31 please?


 drivers/pci/msi.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index 6f2e629..f5bd1c9 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c

@@ -687,8 +687,8 @@ int pci_msix_table_size(struct pci_dev *dev)
  * indicates the successful configuration of MSI-X capability structure
  * with new allocated MSI-X irqs. A return of < 0 indicates a failure.
  * Or a return of > 0 indicates that driver request is exceeding the

number - * of irqs available. Driver should use the returned value to
re-send - * its request.
+ * of irqs or MSI-X vectors available. Driver should use the returned
value to + * re-send its request.
  **/
 int pci_enable_msix(struct pci_dev* dev, struct msix_entry *entries, int
nvec) {

@@ -704,7 +704,7 @@ int pci_enable_msix(struct pci_dev* dev, struct

msix_entry *entries, int nvec)

 	nr_entries = pci_msix_table_size(dev);
 	if (nvec > nr_entries)
-		return -EINVAL;
+		return nr_entries;

 	/* Check for any invalid entries */
 	for (i = 0; i < nvec; i++) {

-- 
MST