firewire: octlet AT payloads can be stack-allocated

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.
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.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Acked-by: Clemens Ladisch <clemens@ladisch.de>

1 files changed, 1 insertions, 14 deletions

diff --git a/drivers/media/dvb/firewire/firedtv-avc.c b/drivers/media/dvb/firewire/firedtv-avc.c
index fc5ccd8c923a..21c52e3b522e 100644
--- a/drivers/media/dvb/firewire/firedtv-avc.c
+++ b/drivers/media/dvb/firewire/firedtv-avc.c
@@ -1320,14 +1320,10 @@ static int cmp_read(struct firedtv *fdtv, u64 addr, __be32 *data)
 {
         int ret;
 
-        mutex_lock(&fdtv->avc_mutex);
-
         ret = fdtv_read(fdtv, addr, data);
         if (ret < 0)
                 dev_err(fdtv->device, "CMP: read I/O error\n");
 
-        mutex_unlock(&fdtv->avc_mutex);
-
         return ret;
 }
 
@@ -1335,18 +1331,9 @@ static int cmp_lock(struct firedtv *fdtv, u64 addr, __be32 data[])
 {
         int ret;
 
-        mutex_lock(&fdtv->avc_mutex);
-
-        /* data[] is stack-allocated and should not be DMA-mapped. */
-        memcpy(fdtv->avc_data, data, 8);
-
-        ret = fdtv_lock(fdtv, addr, fdtv->avc_data);
+        ret = fdtv_lock(fdtv, addr, data);
         if (ret < 0)
                 dev_err(fdtv->device, "CMP: lock I/O error\n");
-        else
-                memcpy(data, fdtv->avc_data, 8);
-
-        mutex_unlock(&fdtv->avc_mutex);
 
         return ret;
 }