From a64662432200f8af6f67cd3664885a323f6a2f2d Mon Sep 17 00:00:00 2001 From: Finn Thain Date: Sat, 31 Dec 2016 19:56:26 -0500 Subject: via-cuda: Avoid TREQ race condition When a read transaction completes, one of several things will happen: a new transfer is started by the driver, a new transfer request is raised by the Cuda (i.e. TREQ asserted), or both happen at once. When both happen at once, there is a race condition between the TREQ test in the read_done state and the same test in cuda_start(). Moreover, the former test uses a stale TREQ value. Theoretically, this can result in the undesirable outcome that the interrupt handler completes with the state machine 'idle' when it should instead start the next transaction. Avoid this race by calling cuda_start() first and then confirming that it succeeded. If not, test the current TREQ value before entering the 'reading' state. Tested-by: Stan Johnson Signed-off-by: Finn Thain Signed-off-by: Michael Ellerman --- drivers/macintosh/via-cuda.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) (limited to 'drivers/macintosh') diff --git a/drivers/macintosh/via-cuda.c b/drivers/macintosh/via-cuda.c index ae3da6b..3212695 100644 --- a/drivers/macintosh/via-cuda.c +++ b/drivers/macintosh/via-cuda.c @@ -605,12 +605,11 @@ cuda_interrupt(int irq, void *arg) memcpy(ibuf, cuda_rbuf, ibuf_len); } reply_ptr = cuda_rbuf; - if (TREQ_asserted(status)) { + cuda_state = idle; + cuda_start(); + if (cuda_state == idle && TREQ_asserted(in_8(&via[B]))) { assert_TIP(); cuda_state = reading; - } else { - cuda_state = idle; - cuda_start(); } break; -- cgit v1.1