[PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile

On Sun 2011-01-02 10:49:32, David Brown wrote:

On Sun, Jan 02 2011, Pavel Machek wrote:

quoted

quoted

quoted

diff --git a/drivers/char/hvc_dcc.c b/drivers/char/hvc_dcc.c
index 6470f63..155ec10 100644
--- a/drivers/char/hvc_dcc.c
+++ b/drivers/char/hvc_dcc.c

@@ -33,8 +33,7 @@
 static inline u32 __dcc_getstatus(void)
 {
 	u32 __ret;
-
-	asm("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
+	asm volatile("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
 		: "=r" (__ret) : : "cc");
 
 	return __ret;

Is volatile needed here? If __dcc_getstatus() return value is
discarded, we want assembly discarded, right?

That's not really the issue being fixed.  Without the volatile, the
compiler is free to cache and reuse a previously loaded status value.
It is important that the status be read each time.

I don't think there is a way of indicating that assembly needs to happen
for each use, but that it is OK to discard if the value isn't used.
'volatile' is a bit overloaded.

Ok, thanks for explanation.
									Pavel
-- 
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