[Cbe-oss-dev] [PATCH 1/2] spufs: fix update of mailbox status register during backed wbox write

[Jeremy Kerr]

From: Arnd Bergmann <arnd at arndb.de>

When a process writes into the inbound spu mailbox (wbox) while the
context is saved, we accidentally break the contents of the mb_stat_R
register by clearing other entries of the mailbox status register. This
can cause the user side to hang.

This change fixes the problem by only altering the appropriate bits
of the mailbox status register during a backing-store write.

Signed-off-by: Arnd Bergmann <arnd.bergmann at de.ibm.com>
Signed-off-by: Jeremy Kerr <jk at ozlabs.org>

---
 arch/powerpc/platforms/cell/spufs/backing_ops.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/cell/spufs/backing_ops.c b/arch/powerpc/platforms/cell/spufs/backing_ops.c
index 07a0e81..ec01214 100644
--- a/arch/powerpc/platforms/cell/spufs/backing_ops.c
+++ b/arch/powerpc/platforms/cell/spufs/backing_ops.c
@@ -162,7 +162,8 @@ static int spu_backing_wbox_write(struct spu_context *ctx, u32 data)
 		BUG_ON(avail != (4 - slot));
 		ctx->csa.spu_mailbox_data[slot] = data;
 		ctx->csa.spu_chnlcnt_RW[29] = ++slot;
-		ctx->csa.prob.mb_stat_R = (((4 - slot) & 0xff) << 8);
+		ctx->csa.prob.mb_stat_R &= ~(0x00ff00);
+		ctx->csa.prob.mb_stat_R |= (((4 - slot) & 0xff) << 8);
 		gen_spu_event(ctx, MFC_SPU_MAILBOX_WRITTEN_EVENT);
 		ret = 4;
 	} else {