staging: vchiq_arm: Avoid premature message stalls

The constants MAX_COMPLETIONS and MSG_QUEUE_SIZE control
the number of messages that can be outstanding to each client
before the system as a whole stalls. If the numbers are too
small then unnecessary thread switching will occur while
waiting for a (potentially low priority) client thread to
consume some data; badly written clients can even lead to
deadlock.

For services that carry many short messages, 16 messages can
represent a very small amount of data. Since the resources
are small - 16 bytes for a completion, 4 bytes for a message
pointer - increase the limits so they are unlikely to be hit
except in exceptional circumstances.

Signed-off-by: Phil Elwell <phil@raspberrypi.org>
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c

@@ -64,10 +64,10 @@
 #define VCHIQ_MINOR 0
 
 /* Some per-instance constants */
-#define MAX_COMPLETIONS 16
+#define MAX_COMPLETIONS 128
 #define MAX_SERVICES 64
 #define MAX_ELEMENTS 8
-#define MSG_QUEUE_SIZE 64
+#define MSG_QUEUE_SIZE 128
 
 #define KEEPALIVE_VER 1
 #define KEEPALIVE_VER_MIN KEEPALIVE_VER