driver: timing: correctly distribute tseg1 into prop_seg and phase_seg1

Closes #177

driver/ctu_can_fd_hw.c

@@ -356,9 +356,25 @@ void ctu_can_fd_set_nom_bittiming(struct ctucanfd_priv *priv,
 				  const struct can_bittiming *nbt)
 {
 	union ctu_can_fd_btr btr;
-	btr.u32 = 0;
-	btr.s.prop = nbt->prop_seg;
-	btr.s.ph1 = nbt->phase_seg1;
+
+    /*
+     * The timing calculation functions have only constraints on tseg1,
+     * which is prop_seg + phase1_seg combined. tseg1 is then split in half
+     * and stored into prog_seg and phase_seg1. In CTU CAN FD, PROP is 7 bits
+     * wide but PH1 only 6, so we must re-distribute the values here.
+     * TODO: get the fixed values to the kernel, so that they are displayed
+     *       accurately
+     */
+    u32 prop_seg = nbt->prop_seg;
+    u32 phase_seg1 = nbt->phase_seg1;
+    if (phase_seg1 > 63) {
+        prop_seg += phase_seg1 - 63;
+        phase_seg1 = 63;
+    }
+
+    btr.u32 = 0;
+	btr.s.prop = prop_seg;
+	btr.s.ph1 = phase_seg1;
 	btr.s.ph2 = nbt->phase_seg2;
 	btr.s.brp = nbt->brp;
 	btr.s.sjw = nbt->sjw;
@@ -370,9 +386,25 @@ void ctu_can_fd_set_data_bittiming(struct ctucanfd_priv *priv,
 				   const struct can_bittiming *dbt)
 {
 	union ctu_can_fd_btr_fd btr_fd;
+
+    /*
+     * The timing calculation functions have only constraints on tseg1,
+     * which is prop_seg + phase1_seg combined. tseg1 is then split in half
+     * and stored into prog_seg and phase_seg1. In CTU CAN FD, PROP_FD is 6 bits
+     * wide but PH1_FD only 5, so we must re-distribute the values here.
+     * TODO: get the fixed values to the kernel, so that they are displayed
+     *       accurately
+     */
+    u32 prop_seg = dbt->prop_seg;
+    u32 phase_seg1 = dbt->phase_seg1;
+    if (phase_seg1 > 31) {
+        prop_seg += phase_seg1 - 31;
+        phase_seg1 = 31;
+    }
+
 	btr_fd.u32 = 0;
-	btr_fd.s.prop_fd = dbt->prop_seg;
-	btr_fd.s.ph1_fd = dbt->phase_seg1;
+	btr_fd.s.prop_fd = prop_seg;
+	btr_fd.s.ph1_fd = phase_seg1;
 	btr_fd.s.ph2_fd = dbt->phase_seg2;
 	btr_fd.s.brp_fd = dbt->brp;
 	btr_fd.s.sjw_fd = dbt->sjw;