Blackfin arch: defines and provides entry points for certain user space functions at fixed addresses

This patch defines (and provides) entry points for certain user space functions
at fixed addresses.  The Blackfin has no usable atomic instructions, but we can
ensure that these code sequences appear atomic from a user space point of view
by detecting when we're in the process of executing them during the interrupt
handler return path.  This allows much more efficient pthread lock
implementations than the bfin_spinlock syscall we're currently using.

Also provided is a small sys_rt_sigreturn stub which can be used by the signal
handler setup code.  The signal.c part will be committed separately.

Signed-off-by: Bernd Schmidt <bernd.schmidt@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/include/asm-blackfin/fixed_code.h b/include/asm-blackfin/fixed_code.h
new file mode 100644
index 000000000000..e6df84ee1557
--- /dev/null
+++ b/include/asm-blackfin/fixed_code.h
@@ -0,0 +1,20 @@
+/* This file defines the fixed addresses where userspace programs can find
+   atomic code sequences.  */
+
+#define FIXED_CODE_START        0x400
+
+#define SIGRETURN_STUB          0x400
+
+#define ATOMIC_SEQS_START       0x410
+
+#define ATOMIC_XCHG32           0x410
+#define ATOMIC_CAS32            0x420
+#define ATOMIC_ADD32            0x430
+#define ATOMIC_SUB32            0x440
+#define ATOMIC_IOR32            0x450
+#define ATOMIC_AND32            0x460
+#define ATOMIC_XOR32            0x470
+
+#define ATOMIC_SEQS_END         0x480
+
+#define FIXED_CODE_END          0x480