Re: [PATCH V3 1/3] block: clear BLK_FEAT_PCI_P2PDMA in blk_stack_limits() for non-supporting devices

Nitesh Shetty
2026-04-17T10:16:26Z

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On 16/04/26 02:26PM, Chaitanya Kulkarni wrote:
>BLK_FEAT_NOWAIT and BLK_FEAT_POLL are cleared in blk_stack_limits()
>when an underlying device does not support them. Apply the same
>treatment to BLK_FEAT_PCI_P2PDMA: stacking drivers set it
>unconditionally and rely on the core to clear it whenever a
>non-supporting member device is stacked.
>
>Signed-off-by: Chaitanya Kulkarni <kch@nvidia.com>
>---
> block/blk-settings.c | 2 ++
> 1 file changed, 2 insertions(+)
>
>diff --git a/block/blk-settings.c b/block/blk-settings.c
>index 78c83817b9d3..8274631290db 100644
>--- a/block/blk-settings.c
>+++ b/block/blk-settings.c
>@@ -795,6 +795,8 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
> t->features &= ~BLK_FEAT_NOWAIT;
> if (!(b->features & BLK_FEAT_POLL))
> t->features &= ~BLK_FEAT_POLL;
>+ if (!(b->features & BLK_FEAT_PCI_P2PDMA))
>+ t->features &= ~BLK_FEAT_PCI_P2PDMA;
>
> t->flags |= (b->flags & BLK_FLAG_MISALIGNED);
I think you need below patch[1] as well to unset this here.
Also I feel better to include Mike,Mikulas and dm-devel mailing list as well.

Thanks,
Nitesh

[1]
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index dc2eff6b739d..0442c1f4c686 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -590,7 +590,8 @@ int dm_split_args(int *argc, char ***argvp, char *input)
static void dm_set_stacking_limits(struct queue_limits *limits)
{
blk_set_stacking_limits(limits);
- limits->features |= BLK_FEAT_IO_STAT | BLK_FEAT_NOWAIT | BLK_FEAT_POLL;
+ limits->features |= BLK_FEAT_IO_STAT | BLK_FEAT_NOWAIT | BLK_FEAT_POLL \
+ BLK_FEAT_PCI_P2PDMA;
}

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