MIPS: BCM47XX: Slightly clean memory detection

Patch was tested on devices with 64 MiB and 256 MiB of RAM.
It documents every part nicely and drops this hacky part of code:
max = off | ((128 << 20) - 1);

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: Hauke Mehrtens <hauke@hauke-m.de>
Patchwork: https://patchwork.linux-mips.org/patch/6808/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 11 insertions, 8 deletions

diff --git a/arch/mips/bcm47xx/prom.c b/arch/mips/bcm47xx/prom.c
index 0af808dfd1ca..1a03a2f43496 100644
--- a/arch/mips/bcm47xx/prom.c
+++ b/arch/mips/bcm47xx/prom.c
@@ -69,15 +69,18 @@ static __init void prom_init_mem(void)
          * BCM47XX uses 128MB for addressing the ram, if the system contains
          * less that that amount of ram it remaps the ram more often into the
          * available space.
-         * Accessing memory after 128MB will cause an exception.
-         * max contains the biggest possible address supported by the platform.
-         * If the method wants to try something above we assume 128MB ram.
          */
-        off = (unsigned long)prom_init;
-        max = off | ((128 << 20) - 1);
-        for (mem = (1 << 20); mem < (128 << 20); mem += (1 << 20)) {
-                if ((off + mem) > max) {
-                        mem = (128 << 20);
+
+        /* Physical address, without mapping to any kernel segment */
+        off = CPHYSADDR((unsigned long)prom_init);
+
+        /* Accessing memory after 128 MiB will cause an exception */
+        max = 128 << 20;
+
+        for (mem = 1 << 20; mem < max; mem += 1 << 20) {
+                /* Loop condition may be not enough, off may be over 1 MiB */
+                if (off + mem >= max) {
+                        mem = max;
                         printk(KERN_DEBUG "assume 128MB RAM\n");
                         break;
                 }