MIPS: c-r4k: Fix size calc when avoiding IPIs for small icache flushes

Commit f70ddc07b637 ("MIPS: c-r4k: Avoid small flush_icache_range SMP
calls") adds checks to force use of hit-type cache ops for small icache
flushes where they are globalised & index-type cache ops aren't, in
order to avoid the overhead of IPIs in those cases. However it
calculated the size of the region being flushed incorrectly, subtracting
the end address from the start address rather than the reverse. This
would have led to an overflow with size wrapping round to some large
value, and likely to the special case for avoiding IPIs not actually
being hit.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: James Hogan <james.hogan@imgtec.com>
Fixes: f70ddc07b637 ("MIPS: c-r4k: Avoid small flush_icache_range SMP calls")
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Cc: Huacai Chen <chenhc@lemote.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/14211/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

diff --git a/arch/mips/mm/c-r4k.c b/arch/mips/mm/c-r4k.c
index cd72805b64a764c0a33f7d7ffb8c10d8119ac509..fa7d8d3790bfc960bc7d4b358e9fb1a5120c04e2 100644 (file)
--- a/arch/mips/mm/c-r4k.c
+++ b/arch/mips/mm/c-r4k.c
@@ -800,7 +800,7 @@ static void r4k_flush_icache_range(unsigned long start, unsigned long end)
                 * If address-based cache ops don't require an SMP call, then
                 * use them exclusively for small flushes.
                 */
-               size = start - end;
+               size = end - start;
                cache_size = icache_size;
                if (!cpu_has_ic_fills_f_dc) {
                        size *= 2;