1 files changed, 23 insertions, 0 deletions

diff --git a/arch/powerpc/platforms/powernv/opal-xscom.c b/arch/powerpc/platforms/powernv/opal-xscom.c
index 09a90d8897ba..4d99a8fd55ac 100644
--- a/arch/powerpc/platforms/powernv/opal-xscom.c
+++ b/arch/powerpc/platforms/powernv/opal-xscom.c
@@ -71,11 +71,33 @@ static int opal_xscom_err_xlate(int64_t rc)
         }
 }
 
+static u64 opal_scom_unmangle(u64 reg)
+{
+        /*
+         * XSCOM indirect addresses have the top bit set. Additionally
+         * the reset of the top 3 nibbles is always 0.
+         *
+         * Because the debugfs interface uses signed offsets and shifts
+         * the address left by 3, we basically cannot use the top 4 bits
+         * of the 64-bit address, and thus cannot use the indirect bit.
+         *
+         * To deal with that, we support the indirect bit being in bit
+         * 4 (IBM notation) instead of bit 0 in this API, we do the
+         * conversion here. To leave room for further xscom address
+         * expansion, we only clear out the top byte
+         *
+         */
+        if (reg & (1ull << 59))
+                reg = (reg & ~(0xffull << 56)) | (1ull << 63);
+        return reg;
+}
+
 static int opal_scom_read(scom_map_t map, u64 reg, u64 *value)
 {
         struct opal_scom_map *m = map;
         int64_t rc;
 
+        reg = opal_scom_unmangle(reg);
         rc = opal_xscom_read(m->chip, m->addr + reg, (uint64_t *)__pa(value));
         return opal_xscom_err_xlate(rc);
 }
@@ -85,6 +107,7 @@ static int opal_scom_write(scom_map_t map, u64 reg, u64 value)
         struct opal_scom_map *m = map;
         int64_t rc;
 
+        reg = opal_scom_unmangle(reg);
         rc = opal_xscom_write(m->chip, m->addr + reg, value);
         return opal_xscom_err_xlate(rc);
 }