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Subject[PATCH v3 07/16] ntb: add check and comment for link up to mw_count() and mw_get_align()
Adds a comment and a check to ntb_mw_get_align() so that it always fails
if the function is called before the link is up.

Also adds a comment to ntb_mw_count() to note that it may return 0 if
it is called before the link is up.

This is to prevent accidental mis-use in clients that are testing
on hardware that this doesn't matter for.

Signed-off-by: Logan Gunthorpe <>
include/linux/ntb.h | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/linux/ntb.h b/include/linux/ntb.h
index 609e232c00da..47f2966cfd7f 100644
--- a/include/linux/ntb.h
+++ b/include/linux/ntb.h
@@ -730,7 +730,8 @@ static inline int ntb_link_disable(struct ntb_dev *ntb)
* Hardware and topology may support a different number of memory windows.
* Moreover different peer devices can support different number of memory
* windows. Simply speaking this method returns the number of possible inbound
- * memory windows to share with specified peer device.
+ * memory windows to share with specified peer device. Note: this may return
+ * zero if the link is not up yet.
* Return: the number of memory windows.
@@ -751,7 +752,7 @@ static inline int ntb_mw_count(struct ntb_dev *ntb, int pidx)
* Get the alignments of an inbound memory window with specified index.
* NULL may be given for any output parameter if the value is not needed.
* The alignment and size parameters may be used for allocation of proper
- * shared memory.
+ * shared memory. Note: this must only be called when the link is up.
* Return: Zero on success, otherwise a negative error number.
@@ -760,6 +761,9 @@ static inline int ntb_mw_get_align(struct ntb_dev *ntb, int pidx, int widx,
resource_size_t *size_align,
resource_size_t *size_max)
+ if (!(ntb_link_is_up(ntb, NULL, NULL) & (1 << pidx)))
+ return -ENOTCONN;
return ntb->ops->mw_get_align(ntb, pidx, widx, addr_align, size_align,
 \ /
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