Distinguish between unsupported and invalid MCS

Previously MCS0 was incorrectly set for some of type1 header values
while according to 3GPP TS 44.060 it can only be set for type3. Fix
this:

* use EGPRS_MCS* constants instead of magic values
* do not set MCS0 for reserved bits values in EGPRS header type1
* return different error codes for invalid and unsupported MCS as well
  as for other decoding errors

Note: there's no need to adjust tests because MCS0 decoding is not
supported but it's better to explicitly distinguish between unsupported
and invalid values nevertheless.

Change-Id: Id665d5c0cf50efa18b1bcbf4f17359418a380f9e
Related: OS#1524

2 files changed, 63 insertions, 59 deletions

diff --git a/src/coding/gsm0503_coding.c b/src/coding/gsm0503_coding.c
index 30ec387b..baf1ce15 100644
--- a/src/coding/gsm0503_coding.c
+++ b/src/coding/gsm0503_coding.c
@@ -24,6 +24,7 @@
 #include <stdint.h>
 #include <string.h>
 #include <stdlib.h>
+#include <errno.h>
 
 #include <osmocom/core/bits.h>
 #include <osmocom/core/conv.h>
@@ -820,15 +821,17 @@ int gsm0503_pdtch_egprs_decode(uint8_t *l2_data, sbit_t *bursts, uint16_t nbits,
 	if ((nbits != GSM0503_GPRS_BURSTS_NBITS) &&
 		(nbits != GSM0503_EGPRS_BURSTS_NBITS)) {
 		/* Invalid EGPRS bit length */
-		return -1;
+		return -EOVERFLOW;
 	}
 
 	hdr = (union gprs_rlc_ul_hdr_egprs *) l2_data;
 	type = egprs_decode_hdr(hdr, bursts, nbits);
 	if (egprs_parse_ul_cps(&cps, hdr, type) < 0)
-		return -1;
+		return -EIO;
 
 	switch (cps.mcs) {
+	case EGPRS_MCS0:
+		return -ENOTSUP;
 	case EGPRS_MCS1:
 	case EGPRS_MCS2:
 	case EGPRS_MCS3:
@@ -846,7 +849,7 @@ int gsm0503_pdtch_egprs_decode(uint8_t *l2_data, sbit_t *bursts, uint16_t nbits,
 		break;
 	default:
 		/* Invalid MCS-X */
-		return -1;
+		return -EINVAL;
 	}
 
 	/* Decode MCS-X block, where X = cps.mcs */
@@ -854,19 +857,19 @@ int gsm0503_pdtch_egprs_decode(uint8_t *l2_data, sbit_t *bursts, uint16_t nbits,
 		rc = egprs_decode_data(l2_data, dc, cps.mcs, cps.p[0],
 			0, n_errors, n_bits_total);
 		if (rc < 0)
-			return -1;
+			return -EFAULT;
 	} else {
 		/* MCS-7,8,9 block 1 */
 		rc = egprs_decode_data(l2_data, c1, cps.mcs, cps.p[0],
 			0, n_errors, n_bits_total);
 		if (rc < 0)
-			return -1;
+			return -EFAULT;
 
 		/* MCS-7,8,9 block 2 */
 		rc = egprs_decode_data(l2_data, c2, cps.mcs, cps.p[1],
 			1, n_errors, n_bits_total);
 		if (rc < 0)
-			return -1;
+			return -EFAULT;
 	}
 
 	return rc;
diff --git a/src/gsm/gprs_rlc.c b/src/gsm/gprs_rlc.c
index d6ccbbe4..a4053ef6 100644
--- a/src/gsm/gprs_rlc.c
+++ b/src/gsm/gprs_rlc.c
@@ -2,6 +2,7 @@
 #include <string.h>
 
 #include <osmocom/gprs/gprs_rlc.h>
+#include <osmocom/coding/gsm0503_coding.h>
 #include <osmocom/gprs/protocol/gsm_04_60.h>
 
 #define EGPRS_CPS_TYPE1_TBL_SZ		29
@@ -10,35 +11,35 @@
 
 /* 3GPP TS 44.060 10.4.8a.1.1 "Header type 1" */
 static const struct egprs_cps egprs_cps_table_type1[EGPRS_CPS_TYPE1_TBL_SZ] = {
-	{ .bits =  0, .mcs = 9, .p = { EGPRS_CPS_P1, EGPRS_CPS_P1 } },
-	{ .bits =  1, .mcs = 9, .p = { EGPRS_CPS_P1, EGPRS_CPS_P2 } },
-	{ .bits =  2, .mcs = 9, .p = { EGPRS_CPS_P1, EGPRS_CPS_P3 } },
-	{ .bits =  3, .mcs = 0, .p = { EGPRS_CPS_NONE, EGPRS_CPS_NONE } },
-	{ .bits =  4, .mcs = 9, .p = { EGPRS_CPS_P2, EGPRS_CPS_P1 } },
-	{ .bits =  5, .mcs = 9, .p = { EGPRS_CPS_P2, EGPRS_CPS_P2 } },
-	{ .bits =  6, .mcs = 9, .p = { EGPRS_CPS_P2, EGPRS_CPS_P3 } },
-	{ .bits =  7, .mcs = 0, .p = { EGPRS_CPS_NONE, EGPRS_CPS_NONE } },
-	{ .bits =  8, .mcs = 9, .p = { EGPRS_CPS_P3, EGPRS_CPS_P1 } },
-	{ .bits =  9, .mcs = 9, .p = { EGPRS_CPS_P3, EGPRS_CPS_P2 } },
-	{ .bits = 10, .mcs = 9, .p = { EGPRS_CPS_P3, EGPRS_CPS_P3 } },
-	{ .bits = 11, .mcs = 8, .p = { EGPRS_CPS_P1, EGPRS_CPS_P1 } },
-	{ .bits = 12, .mcs = 8, .p = { EGPRS_CPS_P1, EGPRS_CPS_P2 } },
-	{ .bits = 13, .mcs = 8, .p = { EGPRS_CPS_P1, EGPRS_CPS_P3 } },
-	{ .bits = 14, .mcs = 8, .p = { EGPRS_CPS_P2, EGPRS_CPS_P1 } },
-	{ .bits = 15, .mcs = 8, .p = { EGPRS_CPS_P2, EGPRS_CPS_P2 } },
-	{ .bits = 16, .mcs = 8, .p = { EGPRS_CPS_P2, EGPRS_CPS_P3 } },
-	{ .bits = 17, .mcs = 8, .p = { EGPRS_CPS_P3, EGPRS_CPS_P1 } },
-	{ .bits = 18, .mcs = 8, .p = { EGPRS_CPS_P3, EGPRS_CPS_P2 } },
-	{ .bits = 19, .mcs = 8, .p = { EGPRS_CPS_P3, EGPRS_CPS_P3 } },
-	{ .bits = 20, .mcs = 7, .p = { EGPRS_CPS_P1, EGPRS_CPS_P1 } },
-	{ .bits = 21, .mcs = 7, .p = { EGPRS_CPS_P1, EGPRS_CPS_P2 } },
-	{ .bits = 22, .mcs = 7, .p = { EGPRS_CPS_P1, EGPRS_CPS_P3 } },
-	{ .bits = 23, .mcs = 7, .p = { EGPRS_CPS_P2, EGPRS_CPS_P1 } },
-	{ .bits = 24, .mcs = 7, .p = { EGPRS_CPS_P2, EGPRS_CPS_P2 } },
-	{ .bits = 25, .mcs = 7, .p = { EGPRS_CPS_P2, EGPRS_CPS_P3 } },
-	{ .bits = 26, .mcs = 7, .p = { EGPRS_CPS_P3, EGPRS_CPS_P1 } },
-	{ .bits = 27, .mcs = 7, .p = { EGPRS_CPS_P3, EGPRS_CPS_P2 } },
-	{ .bits = 28, .mcs = 7, .p = { EGPRS_CPS_P3, EGPRS_CPS_P3 } },
+	{ .bits =  0, .mcs = EGPRS_MCS9, .p = { EGPRS_CPS_P1, EGPRS_CPS_P1 } },
+	{ .bits =  1, .mcs = EGPRS_MCS9, .p = { EGPRS_CPS_P1, EGPRS_CPS_P2 } },
+	{ .bits =  2, .mcs = EGPRS_MCS9, .p = { EGPRS_CPS_P1, EGPRS_CPS_P3 } },
+	{ .bits =  3, .mcs = EGPRS_NUM_MCS, .p = { EGPRS_CPS_NONE, EGPRS_CPS_NONE } }, /* reserved for future use */
+	{ .bits =  4, .mcs = EGPRS_MCS9, .p = { EGPRS_CPS_P2, EGPRS_CPS_P1 } },
+	{ .bits =  5, .mcs = EGPRS_MCS9, .p = { EGPRS_CPS_P2, EGPRS_CPS_P2 } },
+	{ .bits =  6, .mcs = EGPRS_MCS9, .p = { EGPRS_CPS_P2, EGPRS_CPS_P3 } },
+	{ .bits =  7, .mcs = EGPRS_NUM_MCS, .p = { EGPRS_CPS_NONE, EGPRS_CPS_NONE } }, /* reserved for future use */
+	{ .bits =  8, .mcs = EGPRS_MCS9, .p = { EGPRS_CPS_P3, EGPRS_CPS_P1 } },
+	{ .bits =  9, .mcs = EGPRS_MCS9, .p = { EGPRS_CPS_P3, EGPRS_CPS_P2 } },
+	{ .bits = 10, .mcs = EGPRS_MCS9, .p = { EGPRS_CPS_P3, EGPRS_CPS_P3 } },
+	{ .bits = 11, .mcs = EGPRS_MCS8, .p = { EGPRS_CPS_P1, EGPRS_CPS_P1 } },
+	{ .bits = 12, .mcs = EGPRS_MCS8, .p = { EGPRS_CPS_P1, EGPRS_CPS_P2 } },
+	{ .bits = 13, .mcs = EGPRS_MCS8, .p = { EGPRS_CPS_P1, EGPRS_CPS_P3 } },
+	{ .bits = 14, .mcs = EGPRS_MCS8, .p = { EGPRS_CPS_P2, EGPRS_CPS_P1 } },
+	{ .bits = 15, .mcs = EGPRS_MCS8, .p = { EGPRS_CPS_P2, EGPRS_CPS_P2 } },
+	{ .bits = 16, .mcs = EGPRS_MCS8, .p = { EGPRS_CPS_P2, EGPRS_CPS_P3 } },
+	{ .bits = 17, .mcs = EGPRS_MCS8, .p = { EGPRS_CPS_P3, EGPRS_CPS_P1 } },
+	{ .bits = 18, .mcs = EGPRS_MCS8, .p = { EGPRS_CPS_P3, EGPRS_CPS_P2 } },
+	{ .bits = 19, .mcs = EGPRS_MCS8, .p = { EGPRS_CPS_P3, EGPRS_CPS_P3 } },
+	{ .bits = 20, .mcs = EGPRS_MCS7, .p = { EGPRS_CPS_P1, EGPRS_CPS_P1 } },
+	{ .bits = 21, .mcs = EGPRS_MCS7, .p = { EGPRS_CPS_P1, EGPRS_CPS_P2 } },
+	{ .bits = 22, .mcs = EGPRS_MCS7, .p = { EGPRS_CPS_P1, EGPRS_CPS_P3 } },
+	{ .bits = 23, .mcs = EGPRS_MCS7, .p = { EGPRS_CPS_P2, EGPRS_CPS_P1 } },
+	{ .bits = 24, .mcs = EGPRS_MCS7, .p = { EGPRS_CPS_P2, EGPRS_CPS_P2 } },
+	{ .bits = 25, .mcs = EGPRS_MCS7, .p = { EGPRS_CPS_P2, EGPRS_CPS_P3 } },
+	{ .bits = 26, .mcs = EGPRS_MCS7, .p = { EGPRS_CPS_P3, EGPRS_CPS_P1 } },
+	{ .bits = 27, .mcs = EGPRS_MCS7, .p = { EGPRS_CPS_P3, EGPRS_CPS_P2 } },
+	{ .bits = 28, .mcs = EGPRS_MCS7, .p = { EGPRS_CPS_P3, EGPRS_CPS_P3 } },
 };
 
 /*
@@ -46,34 +47,34 @@ static const struct egprs_cps egprs_cps_table_type1[EGPRS_CPS_TYPE1_TBL_SZ] = {
  * "Header type 2 in EGPRS TBF or uplink EGPRS2-A TBF"
  */
 static const struct egprs_cps egprs_cps_table_type2[EGPRS_CPS_TYPE2_TBL_SZ] = {
-	{ .bits =  0, .mcs = 6, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
-	{ .bits =  1, .mcs = 6, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
-	{ .bits =  2, .mcs = 6, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
-	{ .bits =  3, .mcs = 6, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
-	{ .bits =  4, .mcs = 5, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
-	{ .bits =  5, .mcs = 5, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
-	{ .bits =  6, .mcs = 6, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
-	{ .bits =  7, .mcs = 6, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
+	{ .bits =  0, .mcs = EGPRS_MCS6, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
+	{ .bits =  1, .mcs = EGPRS_MCS6, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
+	{ .bits =  2, .mcs = EGPRS_MCS6, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
+	{ .bits =  3, .mcs = EGPRS_MCS6, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
+	{ .bits =  4, .mcs = EGPRS_MCS5, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
+	{ .bits =  5, .mcs = EGPRS_MCS5, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
+	{ .bits =  6, .mcs = EGPRS_MCS6, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
+	{ .bits =  7, .mcs = EGPRS_MCS6, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
 };
 
 /* 3GPP TS 44.060 10.4.8a.3 "Header type 3" */
 static const struct egprs_cps egprs_cps_table_type3[EGPRS_CPS_TYPE3_TBL_SZ] = {
-	{ .bits =  0, .mcs = 4, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
-	{ .bits =  1, .mcs = 4, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
-	{ .bits =  2, .mcs = 4, .p = { EGPRS_CPS_P3, EGPRS_CPS_NONE } },
-	{ .bits =  3, .mcs = 3, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
-	{ .bits =  4, .mcs = 3, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
-	{ .bits =  5, .mcs = 3, .p = { EGPRS_CPS_P3, EGPRS_CPS_NONE } },
-	{ .bits =  6, .mcs = 3, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
-	{ .bits =  7, .mcs = 3, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
-	{ .bits =  8, .mcs = 3, .p = { EGPRS_CPS_P3, EGPRS_CPS_NONE } },
-	{ .bits =  9, .mcs = 2, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
-	{ .bits = 10, .mcs = 2, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
-	{ .bits = 11, .mcs = 1, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
-	{ .bits = 12, .mcs = 1, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
-	{ .bits = 13, .mcs = 2, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
-	{ .bits = 14, .mcs = 2, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
-	{ .bits = 15, .mcs = 0, .p = { EGPRS_CPS_NONE, EGPRS_CPS_NONE } },
+	{ .bits =  0, .mcs = EGPRS_MCS4, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
+	{ .bits =  1, .mcs = EGPRS_MCS4, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
+	{ .bits =  2, .mcs = EGPRS_MCS4, .p = { EGPRS_CPS_P3, EGPRS_CPS_NONE } },
+	{ .bits =  3, .mcs = EGPRS_MCS3, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
+	{ .bits =  4, .mcs = EGPRS_MCS3, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
+	{ .bits =  5, .mcs = EGPRS_MCS3, .p = { EGPRS_CPS_P3, EGPRS_CPS_NONE } },
+	{ .bits =  6, .mcs = EGPRS_MCS3, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
+	{ .bits =  7, .mcs = EGPRS_MCS3, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
+	{ .bits =  8, .mcs = EGPRS_MCS3, .p = { EGPRS_CPS_P3, EGPRS_CPS_NONE } },
+	{ .bits =  9, .mcs = EGPRS_MCS2, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
+	{ .bits = 10, .mcs = EGPRS_MCS2, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
+	{ .bits = 11, .mcs = EGPRS_MCS1, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
+	{ .bits = 12, .mcs = EGPRS_MCS1, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
+	{ .bits = 13, .mcs = EGPRS_MCS2, .p = { EGPRS_CPS_P1, EGPRS_CPS_NONE } },
+	{ .bits = 14, .mcs = EGPRS_MCS2, .p = { EGPRS_CPS_P2, EGPRS_CPS_NONE } },
+	{ .bits = 15, .mcs = EGPRS_MCS0, .p = { EGPRS_CPS_NONE, EGPRS_CPS_NONE } },
 };
 
 int egprs_get_cps(struct egprs_cps *cps, uint8_t type, uint8_t bits)