immap_8260.h: volatile missing in immr definition

immap_8260.h: volatile missing in immr definition

[Hans dot Feldt at uab.ericsson.se]

I've been trying to get the watchdog timer to run in a 2.4.18 kernel
on our custom 750/8260 board. Finally I realised what was the problem
by disassembling with objdump. Due to the missing volatile declaration,
the dog kicking code

	immr->im_siu_conf.sc_swsr = 0x556c;
	immr->im_siu_conf.sc_swsr = 0xaa39;

gets optimised into this by gcc:
	immr->im_siu_conf.sc_swsr = 0xaa39;

which don't make the dog happy.

Sorry if this is an old issue, I searched for it and couldn't find
anything. The patches for 2.4.18 does not contain this fix.

I don't know how it works but could someone who feel responsible change
the original source please?

Change from: extern immap_t *immr:
to: extern volatile immap_t *immr;

The actual variable declaration in 8260_io/commproc.c should probably
be volatiled to.

The system now boots with a 1.8s watchdog timer!

Cheers,
Hans


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Re: immap_8260.h: volatile missing in immr definition

[Dan Malek]

Hans dot Feldt at uab.ericsson.se wrote:

> Change from: extern immap_t *immr:
> to: extern volatile immap_t *immr;

Rather than do this, I would prefer you use a function local variable
and load the global immr into it.  You should also get into the habit
of using barrier operations between such I/O accesses that must be
properly ordered.  The global volatile declaration isn't sufficient
to enforce ordered operations.  You just got lucky this time.

Thanks.


	-- Dan


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