net: ipa: program metadata mask differently

The way the mask value is programmed for QMAP RX endpoints was based
on some wrong assumptions about the way metadata containing the QMAP
mux_id value is formatted. The metadata value supplied by the
modem is *not* in QMAP format, and in fact contains the mux_id we
want in its (big endian) low-order byte. That byte must be written
by the IPA into offset 1 of the QMAP header it inserts before the
received packet.

QMAP TX endpoints *do* use a QMAP header as the metadata sent with
each packet. The modem assumes this, and based on that assumes the
mux_id is in the second byte. To match those assumptions we must
program the modem TX (QMAP) endpoint HDR register to indicate the
metadata will be found at offset 0 in the message header.

The previous configuration managed to work, but it was not working
correctly. This patch fixes a bug whose symptom was receipt of
messages containing the wrong QMAP mux_id.

In fixing this, get rid of ipa_rmnet_mux_id_metadata_mask(), which
was more or less defined so there was a separate place to explain
what was happening as we generated the mask value. Instead, put a
longer description of how this works above ipa_endpoint_init_hdr(),
and define the metadata mask to use as a simple constant.

Signed-off-by: Alex Elder <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ipa/ipa_endpoint.c

···
 /* The amount of RX buffer space consumed by standard skb overhead */
 #define IPA_RX_BUFFER_OVERHEAD	(PAGE_SIZE - SKB_MAX_ORDER(NET_SKB_PAD, 0))
 
+/* Where to find the QMAP mux_id for a packet within modem-supplied metadata */
+#define IPA_ENDPOINT_QMAP_METADATA_MASK		0x000000ff /* host byte order */
+
 #define IPA_ENDPOINT_RESET_AGGR_RETRY_MAX	3
 #define IPA_AGGR_TIME_LIMIT_DEFAULT		1000	/* microseconds */
 
···
 	iowrite32(val, endpoint->ipa->reg_virt + offset);
 }
 
+/**
+ * We program QMAP endpoints so each packet received is preceded by a QMAP
+ * header structure.  The QMAP header contains a 1-byte mux_id and 2-byte
+ * packet size field, and we have the IPA hardware populate both for each
+ * received packet.  The header is configured (in the HDR_EXT register)
+ * to use big endian format.
+ *
+ * The packet size is written into the QMAP header's pkt_len field.  That
+ * location is defined here using the HDR_OFST_PKT_SIZE field.
+ *
+ * The mux_id comes from a 4-byte metadata value supplied with each packet
+ * by the modem.  It is *not* a QMAP header, but it does contain the mux_id
+ * value that we want, in its low-order byte.  A bitmask defined in the
+ * endpoint's METADATA_MASK register defines which byte within the modem
+ * metadata contains the mux_id.  And the OFST_METADATA field programmed
+ * here indicates where the extracted byte should be placed within the QMAP
+ * header.
+ */
 static void ipa_endpoint_init_hdr(struct ipa_endpoint *endpoint)
 {
 	u32 offset = IPA_REG_ENDP_INIT_HDR_N_OFFSET(endpoint->endpoint_id);
···
 	if (endpoint->data->qmap) {
 		size_t header_size = sizeof(struct rmnet_map_header);
 
+		/* We might supply a checksum header after the QMAP header */
 		if (endpoint->toward_ipa && endpoint->data->checksum)
 			header_size += sizeof(struct rmnet_map_ul_csum_header);
-
 		val |= u32_encode_bits(header_size, HDR_LEN_FMASK);
-		/* metadata is the 4 byte rmnet_map header itself */
-		val |= HDR_OFST_METADATA_VALID_FMASK;
-		val |= u32_encode_bits(0, HDR_OFST_METADATA_FMASK);
-		/* HDR_ADDITIONAL_CONST_LEN is 0; (IPA->AP only) */
-		if (!endpoint->toward_ipa) {
-			u32 size_offset = offsetof(struct rmnet_map_header,
-						   pkt_len);
 
+		/* Define how to fill mux_id in a received QMAP header */
+		if (!endpoint->toward_ipa) {
+			u32 off;	/* Field offset within header */
+
+			/* Where IPA will write the metadata value */
+			off = offsetof(struct rmnet_map_header, mux_id);
+			val |= u32_encode_bits(off, HDR_OFST_METADATA_FMASK);
+
+			/* Where IPA will write the length */
+			off = offsetof(struct rmnet_map_header, pkt_len);
 			val |= HDR_OFST_PKT_SIZE_VALID_FMASK;
-			val |= u32_encode_bits(size_offset,
-					       HDR_OFST_PKT_SIZE_FMASK);
+			val |= u32_encode_bits(off, HDR_OFST_PKT_SIZE_FMASK);
 		}
+		/* For QMAP TX, metadata offset is 0 (modem assumes this) */
+		val |= HDR_OFST_METADATA_VALID_FMASK;
+
+		/* HDR_ADDITIONAL_CONST_LEN is 0; (RX only) */
 		/* HDR_A5_MUX is 0 */
 		/* HDR_LEN_INC_DEAGG_HDR is 0 */
-		/* HDR_METADATA_REG_VALID is 0; (AP->IPA only) */
+		/* HDR_METADATA_REG_VALID is 0 (TX only) */
 	}
 
 	iowrite32(val, endpoint->ipa->reg_virt + offset);
···
 	iowrite32(val, endpoint->ipa->reg_virt + offset);
 }
 
-/**
- * Generate a metadata mask value that will select only the mux_id
- * field in an rmnet_map header structure.  The mux_id is at offset
- * 1 byte from the beginning of the structure, but the metadata
- * value is treated as a 4-byte unit.  So this mask must be computed
- * with endianness in mind.  Note that ipa_endpoint_init_hdr_metadata_mask()
- * will convert this value to the proper byte order.
- *
- * Marked __always_inline because this is really computing a
- * constant value.
- */
-static __always_inline __be32 ipa_rmnet_mux_id_metadata_mask(void)
-{
-	size_t mux_id_offset = offsetof(struct rmnet_map_header, mux_id);
-	u32 mux_id_mask = 0;
-	u8 *bytes;
-
-	bytes = (u8 *)&mux_id_mask;
-	bytes[mux_id_offset] = 0xff;	/* mux_id is 1 byte */
-
-	return cpu_to_be32(mux_id_mask);
-}
 
 static void ipa_endpoint_init_hdr_metadata_mask(struct ipa_endpoint *endpoint)
 {
···
 
 	offset = IPA_REG_ENDP_INIT_HDR_METADATA_MASK_N_OFFSET(endpoint_id);
 
+	/* Note that HDR_ENDIANNESS indicates big endian header fields */
 	if (!endpoint->toward_ipa && endpoint->data->qmap)
-		val = ipa_rmnet_mux_id_metadata_mask();
+		val = cpu_to_be32(IPA_ENDPOINT_QMAP_METADATA_MASK);
 
 	iowrite32(val, endpoint->ipa->reg_virt + offset);
 }