[PATCH 6/8] scsi: megaraid: 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: Sreekanth Reddy <sreekanth.reddy at broadcom.com>
Cc: Sathya Prakash Veerichetty <sathya.prakash at broadcom.com>
Cc: Kashyap Desai <kashyap.desai at broadcom.com>
Cc: Sumit Saxena <sumit.saxena at broadcom.com>
Signed-off-by: Ming Lei <ming.lei at redhat.com>
---
 drivers/scsi/megaraid/megaraid_sas_base.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/megaraid/megaraid_sas_base.c b/drivers/scsi/megaraid/megaraid_sas_base.c
index 050eed8e2684..214713803c2e 100644
--- a/drivers/scsi/megaraid/megaraid_sas_base.c
+++ b/drivers/scsi/megaraid/megaraid_sas_base.c
@@ -5921,6 +5921,10 @@ __megasas_alloc_irq_vectors(struct megasas_instance *instance)
 	int i, irq_flags;
 	struct irq_affinity desc = { .pre_vectors = instance->low_latency_index_start };
 	struct irq_affinity *descp = &desc;
+	unsigned max_vecs = instance->msix_vectors - instance->iopoll_q_count;
+
+	if (max_vecs > blk_mq_max_nr_hw_queues())
+		max_vecs = blk_mq_max_nr_hw_queues();
 
 	irq_flags = PCI_IRQ_MSIX;
 
@@ -5934,7 +5938,7 @@ __megasas_alloc_irq_vectors(struct megasas_instance *instance)
 	 */
 	i = pci_alloc_irq_vectors_affinity(instance->pdev,
 		instance->low_latency_index_start,
-		instance->msix_vectors - instance->iopoll_q_count, irq_flags, descp);
+		max_vecs, irq_flags, descp);
 
 	return i;
 }
-- 
2.40.1