Stefan Richter wrote:
...provided that the allocation persists until the packet was sent out to the bus. But we do not need slab allocations anymore in order to satisfy streaming DMA mapping constraints, thanks to commit da28947e7e36 "firewire: ohci: avoid separate DMA mapping for small AT payloads".
(Besides, the slab-allocated buffers that firewire-core, firewire-sbp2, and firedtv used to provide for 8-byte write and lock requests were still not fully portable since they crossed cacheline boundaries or shared a cacheline with unrelated CPU-accessed data. snd-firewire-lib got this aspect right by using an extra kmalloc/ kfree just for the 8-byte transaction buffer.)
This change replaces kmalloc'ed lock transaction scratch buffers in firewire-core, firedtv, and snd-firewire-lib by local stack allocations. The lifetime requirement of these allocations is fulfilled because the call sites use the blocking fw_run_transaction API.
Perhaps the most notable result of the change is simpler locking because there is no need to serialize usages of preallocated per-device buffers anymore. Also, allocations and deallocations are simpler.
firewire-sbp2's struct sbp2_orb.pointer buffer for 8-byte block write requests on the other hand needs to remain slab-allocated in order to keep the allocation around until end of AT DMA.
Signed-off-by: Stefan Richter stefanr@s5r6.in-berlin.de
Acked-by: Clemens Ladisch clemens@ladisch.de