net: ipa: header pad field only valid for AP->modem endpoint

Only QMAP endpoints should be configured to find a pad size field
within packet headers.  They are found in the first byte of the QMAP
header (and the hardware fills only the 6 bits in that byte that
constitute the pad_len field).

The RMNet driver assumes the pad_len field is valid for received
packets, so we want to ensure the pad_len field is filled in that
case.  That driver also assumes the length in the QMAP header
includes the pad bytes.

The RMNet driver does *not* pad the packets it sends, so the pad_len
field can be ignored.

Fix ipa_endpoint_init_hdr_ext() so it only marks the pad field
offset valid for QMAP RX endpoints, and in that case indicates
that the length field in the header includes the pad bytes.
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ipa/ipa_endpoint.c

@@ -467,7 +467,7 @@ static void ipa_endpoint_init_hdr(struct ipa_endpoint *endpoint)
 			header_size += sizeof(struct rmnet_map_ul_csum_header);
 		val |= u32_encode_bits(header_size, HDR_LEN_FMASK);
 
-		/* Define how to fill mux_id in a received QMAP header */
+		/* Define how to fill fields in a received QMAP header */
 		if (!endpoint->toward_ipa) {
 			u32 off;	/* Field offset within header */
 
@@ -499,10 +499,21 @@ static void ipa_endpoint_init_hdr_ext(struct ipa_endpoint *endpoint)
 	u32 val = 0;
 
 	val |= HDR_ENDIANNESS_FMASK;		/* big endian */
-	val |= HDR_TOTAL_LEN_OR_PAD_VALID_FMASK;
-	/* HDR_TOTAL_LEN_OR_PAD is 0 (pad, not total_len) */
+
+	/* A QMAP header contains a 6 bit pad field at offset 0.  The RMNet
+	 * driver assumes this field is meaningful in packets it receives,
+	 * and assumes the header's payload length includes that padding.
+	 * The RMNet driver does *not* pad packets it sends, however, so
+	 * the pad field (although 0) should be ignored.
+	 */
+	if (endpoint->data->qmap && !endpoint->toward_ipa) {
+		val |= HDR_TOTAL_LEN_OR_PAD_VALID_FMASK;
+		/* HDR_TOTAL_LEN_OR_PAD is 0 (pad, not total_len) */
+		val |= HDR_PAYLOAD_LEN_INC_PADDING_FMASK;
+		/* HDR_TOTAL_LEN_OR_PAD_OFFSET is 0 */
+	}
+
 	/* HDR_PAYLOAD_LEN_INC_PADDING is 0 */
-	/* HDR_TOTAL_LEN_OR_PAD_OFFSET is 0 */
 	if (!endpoint->toward_ipa)
 		val |= u32_encode_bits(pad_align, HDR_PAD_TO_ALIGNMENT_FMASK);