[PATCH V3 09/14] scsi: mpt3sas: take blk_mq_max_nr_hw_queues() into account for calculating io vectors

[Ming Lei]

Take blk-mq's knowledge into account for calculating io queues.

Fix wrong queue mapping in case of kdump kernel.

On arm and ppc64, 'maxcpus=1' is passed to kdump kernel command line,
see `Documentation/admin-guide/kdump/kdump.rst`, so num_possible_cpus()
still returns all CPUs because 'maxcpus=1' just bring up one single
cpu core during booting.

blk-mq sees single queue in kdump kernel, and in driver's viewpoint
there are still multiple queues, this inconsistency causes driver to apply
wrong queue mapping for handling IO, and IO timeout is triggered.

Meantime, single queue makes much less resource utilization, and reduce
risk of kernel failure.

Cc: Sathya Prakash <sathya.prakash at broadcom.com>
Cc: Sreekanth Reddy <sreekanth.reddy at broadcom.com>
Cc: Suganath Prabu Subramani <suganath-prabu.subramani at broadcom.com>
Signed-off-by: Ming Lei <ming.lei at redhat.com>
---
 drivers/scsi/mpt3sas/mpt3sas_base.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/mpt3sas/mpt3sas_base.c b/drivers/scsi/mpt3sas/mpt3sas_base.c
index 53f5492579cb..d238e0275edd 100644
--- a/drivers/scsi/mpt3sas/mpt3sas_base.c
+++ b/drivers/scsi/mpt3sas/mpt3sas_base.c
@@ -3332,8 +3332,8 @@ _base_alloc_irq_vectors(struct MPT3SAS_ADAPTER *ioc)
 	 * Don't allocate msix vectors for poll_queues.
 	 * msix_vectors is always within a range of FW supported reply queue.
 	 */
-	int nr_msix_vectors = ioc->iopoll_q_start_index;
-
+	int nr_msix_vectors = min_t(unsigned int, ioc->iopoll_q_start_index,
+			scsi_max_nr_hw_queues());
 
 	if (ioc->smp_affinity_enable)
 		irq_flags |= PCI_IRQ_AFFINITY | PCI_IRQ_ALL_TYPES;
-- 
2.40.1