xtensa: ISS: fix specific simcalls

Simcalls that take memory buffer definitely need wmb or rmb to make sure
gcc doesn't optimize away code that fills the buffer.
Signed-off-by: NMax Filippov <jcmvbkbc@gmail.com>
Signed-off-by: NChris Zankel <chris@zankel.net>

arch/xtensa/platforms/iss/include/platform/simcall.h

@@ -78,8 +78,9 @@ static inline int __simc(int a, int b, int c, int d, int e, int f)
 	return ret;
 }
 
-static inline int simc_open(char *file, int flags, int mode)
+static inline int simc_open(const char *file, int flags, int mode)
 {
+	wmb();
 	return __simc(SYS_open, (int) file, flags, mode, 0, 0);
 }
 
@@ -90,16 +91,19 @@ static inline int simc_close(int fd)
 
 static inline int simc_ioctl(int fd, int request, void *arg)
 {
+	wmb();
 	return __simc(SYS_ioctl, fd, request, (int) arg, 0, 0);
 }
 
 static inline int simc_read(int fd, void *buf, size_t count)
 {
+	rmb();
 	return __simc(SYS_read, fd, (int) buf, count, 0, 0);
 }
 
-static inline int simc_write(int fd, void *buf, size_t count)
+static inline int simc_write(int fd, const void *buf, size_t count)
 {
+	wmb();
 	return __simc(SYS_write, fd, (int) buf, count, 0, 0);
 }
 
@@ -107,6 +111,7 @@ static inline int simc_poll(int fd)
 {
 	struct timeval tv = { .tv_sec = 0, .tv_usec = 0 };
 
+	wmb();
 	return __simc(SYS_select_one, fd, XTISS_SELECT_ONE_READ, (int)&tv,
 			0, 0);
 }