Blackfin arch: Allow ins functions to have a low latency version

Signed-off-by: Robin Getz <rgetz@blackfin.uclinux.org>
Signed-off-by: Bryan Wu <cooloney@kernel.org>

1 files changed, 27 insertions, 0 deletions

diff --git a/arch/blackfin/Kconfig b/arch/blackfin/Kconfig
index cc2add7e39e7..ededf9319f34 100644
--- a/arch/blackfin/Kconfig
+++ b/arch/blackfin/Kconfig
@@ -622,6 +622,33 @@ config CPLB_SWITCH_TAB_L1
           If enabled, the CPLB Switch Tables are linked
           into L1 data memory. (less latency)
 
+comment "Speed Optimizations"
+config BFIN_INS_LOWOVERHEAD
+        bool "ins[bwl] low overhead, higher interrupt latency"
+        default y
+        help
+          Reads on the Blackfin are speculative. In Blackfin terms, this means
+          they can be interrupted at any time (even after they have been issued
+          on to the external bus), and re-issued after the interrupt occurs.
+          For memory - this is not a big deal, since memory does not change if
+          it sees a read.
+
+          If a FIFO is sitting on the end of the read, it will see two reads,
+          when the core only sees one since the FIFO receives both the read
+          which is cancelled (and not delivered to the core) and the one which
+          is re-issued (which is delivered to the core).
+
+          To solve this, interrupts are turned off before reads occur to
+          I/O space. This option controls which the overhead/latency of
+          controlling interrupts during this time
+           "n" turns interrupts off every read
+                (higher overhead, but lower interrupt latency)
+           "y" turns interrupts off every loop
+                (low overhead, but longer interrupt latency)
+
+          default behavior is to leave this set to on (type "Y"). If you are experiencing
+          interrupt latency issues, it is safe and OK to turn this off.
+
 endmenu