net/mlx5: Fix setting of irq->map.index for static IRQ case

When dynamic IRQ allocation is not supported all IRQs are allocated up
front in mlx5_irq_table_create() instead of dynamically as part of
mlx5_irq_alloc(). In the latter dynamic case irq->map.index is set
via the mapping returned by pci_msix_alloc_irq_at(). In the static case
and prior to commit 1da438c0 ("net/mlx5: Fix indexing of mlx5_irq")
irq->map.index was set in mlx5_irq_alloc() twice once initially to 0 and
then to the requested index before storing in the xarray. After this
commit it is only set to 0 which breaks all other IRQ mappings.

Fix this by setting irq->map.index to the requested index together with
irq->map.virq and improve the related comment to make it clearer which
cases it deals with.

Cc: Chuck Lever III <chuck.lever@oracle.com>
Tested-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Eli Cohen <elic@nvidia.com>
Fixes: 1da438c0 ("net/mlx5: Fix indexing of mlx5_irq")
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Tested-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

drivers/net/ethernet/mellanox/mlx5/core/pci_irq.c

@@ -232,12 +232,13 @@ struct mlx5_irq *mlx5_irq_alloc(struct mlx5_irq_pool *pool, int i,
 	if (!irq)
 		return ERR_PTR(-ENOMEM);
 	if (!i || !pci_msix_can_alloc_dyn(dev->pdev)) {
-		/* The vector at index 0 was already allocated.
-		 * Just get the irq number. If dynamic irq is not supported
-		 * vectors have also been allocated.
+		/* The vector at index 0 is always statically allocated. If
+		 * dynamic irq is not supported all vectors are statically
+		 * allocated. In both cases just get the irq number and set
+		 * the index.
 		 */
 		irq->map.virq = pci_irq_vector(dev->pdev, i);
-		irq->map.index = 0;
+		irq->map.index = i;
 	} else {
 		irq->map = pci_msix_alloc_irq_at(dev->pdev, MSI_ANY_INDEX, af_desc);
 		if (!irq->map.virq) {