RE: [PATCH] hpsa: fix boot on ia64 (atomic_t alignment)

From: Don.Brace
Date: Wed Mar 17 2021 - 15:06:56 EST

-----Original Message-----
From: David Laight [mailto:David.Laight@xxxxxxxxxx]
Subject: RE: [PATCH] hpsa: fix boot on ia64 (atomic_t alignment)

From: Martin K. Petersen
> Sent: 17 March 2021 02:26
> Arnd,
> > Actually that still feels wrong: the annotation of the struct is to
> > pack every member, which causes the access to be done in byte units
> > on architectures that do not have hardware unaligned load/store
> > instructions, at least for things like atomic_read() that does not
> > go through a cmpxchg() or ll/sc cycle.
> > This change may fix itanium, but it's still not correct. Other
> > architectures would have already been broken before the recent
> > change, but that's not a reason against fixing them now.
> I agree. I understand why there are restrictions on fields consumed by
> the hardware. But for fields internal to the driver the packing
> doesn't make sense to me.

Jeepers -- that global #pragma pack(1) is bollocks.

I think there are a couple of __u64 that are 32bit aligned.
Just marking those field __packed __aligned(4) should have the desired effect.
Or use a typedef for '__u64 with 32bit alignment'.
(There probably ought to be one in types.h)

Then add compile-time asserts that any non-trivial structures the hardware accesses are the right size.


Don: My dilemma is that hpsa is now a maintenance driver and making more packing/alignment changes would trigger a lot of regression testing. My last patch aligns the structure with what has been in place for a long time now. All I did was rename an unused variable. So making any more changes is not high on my todo list...