pc-bios: s390x: Get rid of magic offsets into the lowcore

If we have a lowcore struct that has members for offsets that we want
to touch, why not use it?

Signed-off-by: Janosch Frank <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Reviewed-by: Thomas Huth <[email protected]>
Reviewed-by: Cornelia Huck <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Thomas Huth <[email protected]>

Author: frankjaa

pc-bios/s390-ccw/cio.h

@@ -122,12 +122,17 @@ typedef struct schib {
 } __attribute__ ((packed, aligned(4))) Schib;
 
 typedef struct subchannel_id {
-        __u32 cssid:8;
-        __u32:4;
-        __u32 m:1;
-        __u32 ssid:2;
-        __u32 one:1;
-        __u32 sch_no:16;
+    union {
+        struct {
+            __u16 cssid:8;
+            __u16 reserved:4;
+            __u16 m:1;
+            __u16 ssid:2;
+            __u16 one:1;
+        };
+        __u16 sch_id;
+    };
+    __u16 sch_no;
 } __attribute__ ((packed, aligned(4))) SubChannelId;
 
 struct chsc_header {

pc-bios/s390-ccw/main.c

@@ -36,11 +36,9 @@ LowCore *lowcore; /* Yes, this *is* a pointer to address 0 */
  */
 void write_subsystem_identification(void)
 {
-    SubChannelId *schid = (SubChannelId *) 184;
-    uint32_t *zeroes = (uint32_t *) 188;
-
-    *schid = blk_schid;
-    *zeroes = 0;
+    lowcore->subchannel_id = blk_schid.sch_id;
+    lowcore->subchannel_nr = blk_schid.sch_no;
+    lowcore->io_int_parm = 0;
 }
 
 void write_iplb_location(void)