ARM unaligned MMIO access with attribute((packed))

From: M?ns Rullg?rd <redacted>
Date: Wed, 02 Feb 2011 23:08:01 +0000

David Miller [off-list ref] writes:

quoted

From: Russell King - ARM Linux <redacted>
Date: Wed, 2 Feb 2011 16:37:02 +0000

quoted

1. there's no way to tell GCC that the inline assembly is a load
   instruction and therefore it needs to schedule the following
   instructions appropriately.

Just add a dummy '"m" (pointer)' asm input argument to the inline asm
statement.  Just make sure "typeof(pointer)" has a size matching the
size of the load your are performing.

That should be "m"(*pointer).

Right, thanks for the correction.

quoted

But you really need that memory clobber there whether you like it or
not, see above.

I don't know of any device where the side-effects are not explicitly
indicated by other means in the code triggering them, so it probably
is safe without the clobber as Russel says.

You're probably right.