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>

3 files changed, 4 insertions, 12 deletions

diff --git a/sound/firewire/cmp.c b/sound/firewire/cmp.c
index 4a37f3a6fab..14cacbc655d 100644
--- a/sound/firewire/cmp.c
+++ b/sound/firewire/cmp.c
@@ -49,10 +49,9 @@ static int pcr_modify(struct cmp_connection *c,
 		      enum bus_reset_handling bus_reset_handling)
 {
 	struct fw_device *device = fw_parent_device(c->resources.unit);
-	__be32 *buffer = c->resources.buffer;
 	int generation = c->resources.generation;
 	int rcode, errors = 0;
-	__be32 old_arg;
+	__be32 old_arg, buffer[2];
 	int err;
 
 	buffer[0] = c->last_pcr_value;
diff --git a/sound/firewire/iso-resources.c b/sound/firewire/iso-resources.c
index 775dbd5f344..bb9c0c1fb52 100644
--- a/sound/firewire/iso-resources.c
+++ b/sound/firewire/iso-resources.c
@@ -11,7 +11,6 @@
 #include <linux/jiffies.h>
 #include <linux/mutex.h>
 #include <linux/sched.h>
-#include <linux/slab.h>
 #include <linux/spinlock.h>
 #include "iso-resources.h"
 
@@ -25,10 +24,6 @@
  */
 int fw_iso_resources_init(struct fw_iso_resources *r, struct fw_unit *unit)
 {
-	r->buffer = kmalloc(2 * 4, GFP_KERNEL);
-	if (!r->buffer)
-		return -ENOMEM;
-
 	r->channels_mask = ~0uLL;
 	r->unit = fw_unit_get(unit);
 	mutex_init(&r->mutex);
@@ -44,7 +39,6 @@ int fw_iso_resources_init(struct fw_iso_resources *r, struct fw_unit *unit)
 void fw_iso_resources_destroy(struct fw_iso_resources *r)
 {
 	WARN_ON(r->allocated);
-	kfree(r->buffer);
 	mutex_destroy(&r->mutex);
 	fw_unit_put(r->unit);
 }
@@ -131,7 +125,7 @@ retry_after_bus_reset:
 
 	bandwidth = r->bandwidth + r->bandwidth_overhead;
 	fw_iso_resource_manage(card, r->generation, r->channels_mask,
-			       &channel, &bandwidth, true, r->buffer);
+			       &channel, &bandwidth, true);
 	if (channel == -EAGAIN) {
 		mutex_unlock(&r->mutex);
 		goto retry_after_bus_reset;
@@ -184,7 +178,7 @@ int fw_iso_resources_update(struct fw_iso_resources *r)
 	bandwidth = r->bandwidth + r->bandwidth_overhead;
 
 	fw_iso_resource_manage(card, r->generation, 1uLL << r->channel,
-			       &channel, &bandwidth, true, r->buffer);
+			       &channel, &bandwidth, true);
 	/*
 	 * When another bus reset happens, pretend that the allocation
 	 * succeeded; we will try again for the new generation later.
@@ -220,7 +214,7 @@ void fw_iso_resources_free(struct fw_iso_resources *r)
 	if (r->allocated) {
 		bandwidth = r->bandwidth + r->bandwidth_overhead;
 		fw_iso_resource_manage(card, r->generation, 1uLL << r->channel,
-				       &channel, &bandwidth, false, r->buffer);
+				       &channel, &bandwidth, false);
 		if (channel < 0)
 			dev_err(&r->unit->device,
 				"isochronous resource deallocation failed\n");
diff --git a/sound/firewire/iso-resources.h b/sound/firewire/iso-resources.h
index 3f0730e4d84..5a9af7c6165 100644
--- a/sound/firewire/iso-resources.h
+++ b/sound/firewire/iso-resources.h
@@ -24,7 +24,6 @@ struct fw_iso_resources {
 	unsigned int bandwidth_overhead;
 	int generation; /* in which allocation is valid */
 	bool allocated;
-	__be32 *buffer;
 };
 
 int fw_iso_resources_init(struct fw_iso_resources *r,