qcacmn: Check boundary conditions while allocating extra buffers

We allocate extra buffers than requested when watermark is less
than critical low threshold. While allocating extra buffers we
should check for boundary conditions so that total allocated
buffers is always within the range of available entries.

Change-Id: I2f24c6157cb2afcc8bc5ca84b7e0308588a4d99d
CRs-Fixed: 3307051

dp/wifi3.0/dp_rx.c

@@ -718,6 +718,7 @@ QDF_STATUS __dp_rx_buffers_replenish(struct dp_soc *dp_soc, uint32_t mac_id,
 	struct dp_pdev *dp_pdev = dp_get_pdev_for_lmac_id(dp_soc, mac_id);
 	uint32_t num_entries_avail;
 	uint32_t count;
+	uint32_t extra_buffers;
 	int sync_hw_ptr = 1;
 	struct dp_rx_nbuf_frag_info nbuf_frag_info = {0};
 	void *rxdma_ring_entry;
@@ -764,11 +765,20 @@ QDF_STATUS __dp_rx_buffers_replenish(struct dp_soc *dp_soc, uint32_t mac_id,
 	} else if ((*desc_list) &&
 		   dp_rxdma_srng->num_entries - num_entries_avail <
 		   CRITICAL_BUFFER_THRESHOLD) {
+		/* set extra buffers to CRITICAL_BUFFER_THRESHOLD only if
+		 * total buff requested after adding extra buffers is less
+		 * than or equal to num entries available, else set it to max
+		 * possible additional buffers available at that moment
+		 */
+		extra_buffers =
+			((num_req_buffers + CRITICAL_BUFFER_THRESHOLD) > num_entries_avail) ?
+			(num_entries_avail - num_req_buffers) :
+			CRITICAL_BUFFER_THRESHOLD;
 		/* Append some free descriptors to tail */
 		num_alloc_desc =
 			dp_rx_get_free_desc_list(dp_soc, mac_id,
 						 rx_desc_pool,
-						 CRITICAL_BUFFER_THRESHOLD,
+						 extra_buffers,
 						 &desc_list_append,
 						 &tail_append);