On Sun, Jan 02 2011, Pavel Machek wrote:
>> > 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.
--
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