net: cdc_ncm: use true max dgram count for header estimates

Many newer NCM and MBIM devices will request a maximum tx
datagram count which is much smaller than our hard-coded
absolute max. We can reduce the overhead without sacrificing
any of the simplicity for these devices, by simply using the
true negotiated count in when calculated the maximum NTH and
NDP header sizes.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 3 deletions

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index 141dbec912be..b9b562b9128a 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -174,7 +174,7 @@ static void cdc_ncm_update_rxtx_max(struct usbnet *dev, u32 new_rx, u32 new_tx)
         }
 
         /* clamp new_tx to sane values */
-        min = CDC_NCM_MIN_HDR_SIZE + ctx->max_datagram_size;
+        min = ctx->max_datagram_size + ctx->max_ndp_size + sizeof(struct usb_cdc_ncm_nth16);
         max = min_t(u32, CDC_NCM_NTB_MAX_SIZE_TX, le32_to_cpu(ctx->ncm_parm.dwNtbOutMaxSize));
 
         /* some devices set dwNtbOutMaxSize too low for the above default */
@@ -318,6 +318,9 @@ static int cdc_ncm_init(struct usbnet *dev)
                         (ctx->tx_max_datagrams > CDC_NCM_DPT_DATAGRAMS_MAX))
                 ctx->tx_max_datagrams = CDC_NCM_DPT_DATAGRAMS_MAX;
 
+        /* set up maximum NDP size */
+        ctx->max_ndp_size = sizeof(struct usb_cdc_ncm_ndp16) + (ctx->tx_max_datagrams + 1) * sizeof(struct usb_cdc_ncm_dpe16);
+
         /* initial coalescing timer interval */
         ctx->timer_interval = CDC_NCM_TIMER_INTERVAL_USEC * NSEC_PER_USEC;
 
@@ -800,7 +803,7 @@ static struct usb_cdc_ncm_ndp16 *cdc_ncm_ndp(struct cdc_ncm_ctx *ctx, struct sk_
         cdc_ncm_align_tail(skb, ctx->tx_ndp_modulus, 0, ctx->tx_max);
 
         /* verify that there is room for the NDP and the datagram (reserve) */
-        if ((ctx->tx_max - skb->len - reserve) < CDC_NCM_NDP_SIZE)
+        if ((ctx->tx_max - skb->len - reserve) < ctx->max_ndp_size)
                 return NULL;
 
         /* link to it */
@@ -810,7 +813,7 @@ static struct usb_cdc_ncm_ndp16 *cdc_ncm_ndp(struct cdc_ncm_ctx *ctx, struct sk_
                 nth16->wNdpIndex = cpu_to_le16(skb->len);
 
         /* push a new empty NDP */
-        ndp16 = (struct usb_cdc_ncm_ndp16 *)memset(skb_put(skb, CDC_NCM_NDP_SIZE), 0, CDC_NCM_NDP_SIZE);
+        ndp16 = (struct usb_cdc_ncm_ndp16 *)memset(skb_put(skb, ctx->max_ndp_size), 0, ctx->max_ndp_size);
         ndp16->dwSignature = sign;
         ndp16->wLength = cpu_to_le16(sizeof(struct usb_cdc_ncm_ndp16) + sizeof(struct usb_cdc_ncm_dpe16));
         return ndp16;