firewire: ohci: use memory barriers to order descriptor updates

When we append to a DMA program, we need to ensure that the order in
which initialization of the new descriptors and update of the
branch_address of the old tail descriptor, as seen by the PCI device,
happen as intended.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

diff --git a/drivers/firewire/ohci.c b/drivers/firewire/ohci.c
index 5f6bb2c53808d49fb11c974f62f6184f25201ec5..3f59d1df6504d8af232bc30756ea135113db7761 100644 (file)
--- a/drivers/firewire/ohci.c
+++ b/drivers/firewire/ohci.c
@@ -595,6 +595,7 @@ static int ar_context_add_page(struct ar_context *ctx)
        ab->descriptor.res_count      = cpu_to_le16(PAGE_SIZE - offset);
        ab->descriptor.branch_address = 0;
 
+       wmb(); /* finish init of new descriptors before branch_address update */
        ctx->last_buffer->descriptor.branch_address = cpu_to_le32(ab_bus | 1);
        ctx->last_buffer->next = ab;
        ctx->last_buffer = ab;
@@ -982,6 +983,8 @@ static void context_append(struct context *ctx,
        d_bus = desc->buffer_bus + (d - desc->buffer) * sizeof(*d);
 
        desc->used += (z + extra) * sizeof(*d);
+
+       wmb(); /* finish init of new descriptors before branch_address update */
        ctx->prev->branch_address = cpu_to_le32(d_bus | z);
        ctx->prev = find_branch_descriptor(d, z);