[PATCH 1/2] md: Add PCI_P2PDMA support for MD RAID volumes

[Chaitanya Kulkarni]

MD RAID does not propagate BLK_FEAT_PCI_P2PDMA from member devices to
the RAID device, preventing peer-to-peer DMA through the RAID layer even
when all underlying devices support it.

Enable BLK_FEAT_PCI_P2PDMA by default in md_init_stacking_limits() and
clear it in mddev_stack_rdev_limits() during array init and 
mddev_stack_new_rdev() during hot-add if any member device lacks support.

Tested with RAID arrays containing multiple NVMe devices with P2PDMA
support, confirming that peer-to-peer transfers work correctly through
the RAID layer.

Signed-off-by: Chaitanya Kulkarni <kch at nvidia.com>
Signed-off-by: Kiran Kumar Modukuri <kmodukuri at nvidia.com>
---
 drivers/md/md.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 521d9b34cd9e..a151ea86d844 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -6176,6 +6176,8 @@ int mddev_stack_rdev_limits(struct mddev *mddev, struct queue_limits *lim,
 		if ((flags & MDDEV_STACK_INTEGRITY) &&
 		    !queue_limits_stack_integrity_bdev(lim, rdev->bdev))
 			return -EINVAL;
+		if (!blk_queue_pci_p2pdma(rdev->bdev->bd_disk->queue))
+			lim->features &= ~BLK_FEAT_PCI_P2PDMA;
 	}
 
 	/*
@@ -6231,6 +6233,8 @@ int mddev_stack_new_rdev(struct mddev *mddev, struct md_rdev *rdev)
 	lim = queue_limits_start_update(mddev->gendisk->queue);
 	queue_limits_stack_bdev(&lim, rdev->bdev, rdev->data_offset,
 				mddev->gendisk->disk_name);
+	if (!blk_queue_pci_p2pdma(rdev->bdev->bd_disk->queue))
+		lim.features &= ~BLK_FEAT_PCI_P2PDMA;
 
 	if (!queue_limits_stack_integrity_bdev(&lim, rdev->bdev)) {
 		pr_err("%s: incompatible integrity profile for %pg\n",
@@ -6272,7 +6276,8 @@ void md_init_stacking_limits(struct queue_limits *lim)
 {
 	blk_set_stacking_limits(lim);
 	lim->features = BLK_FEAT_WRITE_CACHE | BLK_FEAT_FUA |
-			BLK_FEAT_IO_STAT | BLK_FEAT_NOWAIT;
+			BLK_FEAT_IO_STAT | BLK_FEAT_NOWAIT |
+			BLK_FEAT_PCI_P2PDMA;
 }
 EXPORT_SYMBOL_GPL(md_init_stacking_limits);
 
-- 
2.39.5