ntb_transport: Limit memory windows based on available, scratchpads

When the underlying NTB H/W driver advertises more memory windows
than the number of scratchpads available to setup MW's, it is likely
that we may end up filling the remaining memory windows with garbage.
So to avoid that, lets limit the memory windows that transport driver
can setup based on the available scratchpads.

Signed-off-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
Acked-by: Allen Hubbe <Allen.Hubbe@dell.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>

drivers/ntb/ntb_transport.c

@@ -66,6 +66,7 @@
 #define NTB_TRANSPORT_VER	"4"
 #define NTB_TRANSPORT_NAME	"ntb_transport"
 #define NTB_TRANSPORT_DESC	"Software Queue-Pair Transport over NTB"
+#define NTB_TRANSPORT_MIN_SPADS (MW0_SZ_HIGH + 2)
 
 MODULE_DESCRIPTION(NTB_TRANSPORT_DESC);
 MODULE_VERSION(NTB_TRANSPORT_VER);
@@ -242,9 +243,6 @@ enum {
 	NUM_MWS,
 	MW0_SZ_HIGH,
 	MW0_SZ_LOW,
-	MW1_SZ_HIGH,
-	MW1_SZ_LOW,
-	MAX_SPAD,
 };
 
 #define dev_client_dev(__dev) \
@@ -811,7 +809,7 @@ static void ntb_transport_link_cleanup(struct ntb_transport_ctx *nt)
 {
 	struct ntb_transport_qp *qp;
 	u64 qp_bitmap_alloc;
-	int i;
+	unsigned int i, count;
 
 	qp_bitmap_alloc = nt->qp_bitmap & ~nt->qp_bitmap_free;
 
@@ -831,7 +829,8 @@ static void ntb_transport_link_cleanup(struct ntb_transport_ctx *nt)
 	 * goes down, blast them now to give them a sane value the next
 	 * time they are accessed
 	 */
-	for (i = 0; i < MAX_SPAD; i++)
+	count = ntb_spad_count(nt->ndev);
+	for (i = 0; i < count; i++)
 		ntb_spad_write(nt->ndev, i, 0);
 }
 
@@ -1064,17 +1063,12 @@ static int ntb_transport_probe(struct ntb_client *self, struct ntb_dev *ndev)
 {
 	struct ntb_transport_ctx *nt;
 	struct ntb_transport_mw *mw;
-	unsigned int mw_count, qp_count;
+	unsigned int mw_count, qp_count, spad_count, max_mw_count_for_spads;
 	u64 qp_bitmap;
 	int node;
 	int rc, i;
 
 	mw_count = ntb_mw_count(ndev);
-	if (ntb_spad_count(ndev) < (NUM_MWS + 1 + mw_count * 2)) {
-		dev_err(&ndev->dev, "Not enough scratch pad registers for %s",
-			NTB_TRANSPORT_NAME);
-		return -EIO;
-	}
 
 	if (ntb_db_is_unsafe(ndev))
 		dev_dbg(&ndev->dev,
@@ -1090,8 +1084,18 @@ static int ntb_transport_probe(struct ntb_client *self, struct ntb_dev *ndev)
 		return -ENOMEM;
 
 	nt->ndev = ndev;
+	spad_count = ntb_spad_count(ndev);
+
+	/* Limit the MW's based on the availability of scratchpads */
+
+	if (spad_count < NTB_TRANSPORT_MIN_SPADS) {
+		nt->mw_count = 0;
+		rc = -EINVAL;
+		goto err;
+	}
 
-	nt->mw_count = mw_count;
+	max_mw_count_for_spads = (spad_count - MW0_SZ_HIGH) / 2;
+	nt->mw_count = min(mw_count, max_mw_count_for_spads);
 
 	nt->mw_vec = kzalloc_node(mw_count * sizeof(*nt->mw_vec),
 				  GFP_KERNEL, node);