ARM: OMAP: Cleanup OMAP FB SDRAM reservation

The logic in this file is rather convoluted, but essentially:

1. region type 0 is SDRAM
2. referring to the code fragment
                if (set_fbmem_region_type(&rg, OMAPFB_MEMTYPE_SDRAM,
                                          sdram_start, sdram_size) < 0 ||
                    (rg.type != OMAPFB_MEMTYPE_SDRAM))
                        continue;
   - if rg.type is not OMAPFB_MEMTYPE_SDRAM, set_fbmem_region_type()
     returns zero immediately (since rg.type is non-zero), and so we
     'continue'.
   - if rg.type is OMAPFB_MEMTYPE_SDRAM, and rg.paddr is zero,
     we fall through.
   - if rg.type is OMAPFB_MEMTYPE_SDRAM, and the region lies within
     SDRAM, we fall through.
   - if rg.type is OMAPFB_MEMTYPE_SDRAM, and the region is not within
     SDRAM, we 'continue'.
3. check_fbmem_region seems unnecessary.
   - we know rg.type is OMAPFB_MEMTYPE_SDRAM
   - we can check rg.size independently
   - bootmem_reserve() can check for overlapping reservations itself
   - we've already validated that the requested region lies within SDRAM.
4. avoid BUG()ing if the region entry is already set; print an error,
   and mark the configuration invalid - at least we'll continue booting
   so the error message has a chance of being logged/visible via serial
   console.

With these changes in place, it makes the code much easier to understand
and hence easier to convert to LMB.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/plat-omap/fb.c

@@ -171,49 +171,76 @@ static int check_fbmem_region(int region_idx, struct omapfb_mem_region *rg,
 	return 0;
 }
 
+static int valid_sdram(unsigned long addr, unsigned long size)
+{
+	struct bootmem_data *bdata = NODE_DATA(0)->bdata;
+	unsigned long sdram_start, sdram_end;
+
+	sdram_start = bdata->node_min_pfn << PAGE_SHIFT;
+	sdram_end = bdata->node_low_pfn << PAGE_SHIFT;
+
+	return addr >= sdram_start && sdram_end - addr >= size;
+}
+
+static int reserve_sdram(unsigned long addr, unsigned long size)
+{
+	return reserve_bootmem(addr, size, BOOTMEM_EXCLUSIVE);
+}
+
 /*
  * Called from map_io. We need to call to this early enough so that we
  * can reserve the fixed SDRAM regions before VM could get hold of them.
  */
 void __init omapfb_reserve_sdram(void)
 {
-	struct bootmem_data	*bdata;
-	unsigned long		sdram_start, sdram_size;
-	unsigned long		reserved;
-	int			i;
+	unsigned long reserved = 0;
+	int i;
 
 	if (config_invalid)
 		return;
 
-	bdata = NODE_DATA(0)->bdata;
-	sdram_start = bdata->node_min_pfn << PAGE_SHIFT;
-	sdram_size = (bdata->node_low_pfn << PAGE_SHIFT) - sdram_start;
-	reserved = 0;
 	for (i = 0; ; i++) {
-		struct omapfb_mem_region	rg;
+		struct omapfb_mem_region rg;
 
 		if (get_fbmem_region(i, &rg) < 0)
 			break;
+
 		if (i == OMAPFB_PLANE_NUM) {
-			printk(KERN_ERR
-				"Extraneous FB mem configuration entries\n");
+			pr_err("Extraneous FB mem configuration entries\n");
 			config_invalid = 1;
 			return;
 		}
+
 		/* Check if it's our memory type. */
-		if (set_fbmem_region_type(&rg, OMAPFB_MEMTYPE_SDRAM,
-				          sdram_start, sdram_size) < 0 ||
-		    (rg.type != OMAPFB_MEMTYPE_SDRAM))
+		if (rg.type != OMAPFB_MEMTYPE_SDRAM)
 			continue;
-		BUG_ON(omapfb_config.mem_desc.region[i].size);
-		if (check_fbmem_region(i, &rg, sdram_start, sdram_size) < 0) {
+
+		/* Check if the region falls within SDRAM */
+		if (rg.paddr && !valid_sdram(rg.paddr, rg.size))
+			continue;
+
+		if (rg.size == 0) {
+			pr_err("Zero size for FB region %d\n", i);
 			config_invalid = 1;
 			return;
 		}
+
 		if (rg.paddr) {
-			reserve_bootmem(rg.paddr, rg.size, BOOTMEM_DEFAULT);
+			if (reserve_sdram(rg.paddr, rg.size)) {
+				pr_err("Trying to use reserved memory for FB region %d\n",
+					i);
+				config_invalid = 1;
+				return;
+			}
 			reserved += rg.size;
 		}
+
+		if (omapfb_config.mem_desc.region[i].size) {
+			pr_err("FB region %d already set\n", i);
+			config_invalid = 1;
+			return;
+		}
+
 		omapfb_config.mem_desc.region[i] = rg;
 		configured_regions++;
 	}