powerpc: prom_init exception when updating core value

Since the CPU is generating an exception when accessing unaligned word, and
as this exception is not yet handled when running prom_init, data should be
copied from the architecture vector byte per byte.

Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 22 insertions, 6 deletions

diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
index 5fe2842e8bab..cb64a6e1dc51 100644
--- a/arch/powerpc/kernel/prom_init.c
+++ b/arch/powerpc/kernel/prom_init.c
@@ -858,7 +858,8 @@ static void __init prom_send_capabilities(void)
 {
         ihandle root;
         prom_arg_t ret;
-        __be32 *cores;
+        u32 cores;
+        unsigned char *ptcores;
 
         root = call_prom("open", 1, 1, ADDR("/"));
         if (root != 0) {
@@ -868,15 +869,30 @@ static void __init prom_send_capabilities(void)
                  * (we assume this is the same for all cores) and use it to
                  * divide NR_CPUS.
                  */
-                cores = (__be32 *)&ibm_architecture_vec[IBM_ARCH_VEC_NRCORES_OFFSET];
-                if (be32_to_cpup(cores) != NR_CPUS) {
+
+                /* The core value may start at an odd address. If such a word
+                 * access is made at a cache line boundary, this leads to an
+                 * exception which may not be handled at this time.
+                 * Forcing a per byte access to avoid exception.
+                 */
+                ptcores = &ibm_architecture_vec[IBM_ARCH_VEC_NRCORES_OFFSET];
+                cores = 0;
+                cores |= ptcores[0] << 24;
+                cores |= ptcores[1] << 16;
+                cores |= ptcores[2] << 8;
+                cores |= ptcores[3];
+                if (cores != NR_CPUS) {
                         prom_printf("WARNING ! "
                                     "ibm_architecture_vec structure inconsistent: %lu!\n",
-                                    be32_to_cpup(cores));
+                                    cores);
                 } else {
-                        *cores = cpu_to_be32(DIV_ROUND_UP(NR_CPUS, prom_count_smt_threads()));
+                        cores = DIV_ROUND_UP(NR_CPUS, prom_count_smt_threads());
                         prom_printf("Max number of cores passed to firmware: %lu (NR_CPUS = %lu)\n",
-                                    be32_to_cpup(cores), NR_CPUS);
+                                    cores, NR_CPUS);
+                        ptcores[0] = (cores >> 24) & 0xff;
+                        ptcores[1] = (cores >> 16) & 0xff;
+                        ptcores[2] = (cores >> 8) & 0xff;
+                        ptcores[3] = cores & 0xff;
                 }
 
                 /* try calling the ibm,client-architecture-support method */