Re: [PATCH 1/2] pci: Block config access during BIST (resend)

[Paul Mackerras <paulus@samba.org>]

Grant Grundler writes:

> Ok this is good example - I see what the problem is.
> You could use the following sequence too then:
> 	pci_block_user_cfg_access
> 		pci_save_state
> 		block_ucfg_access = 1
> 		mb()
> 		while (spin_is_locked(&pci_lock))
> 			relax_cpu();
> 
> Think this is sufficient?

Maybe, but it seems like a bad idea to me.  It's longer, it's less
obvious what's happening, and it precludes the sorts of optimization
that we do on ppc64 where a cpu that is waiting for a lock can tell
give its time slice to the cpu that is holding the lock (on systems
where the hypervisor time-slices multiple virtual cpus on one physical
cpu).

What's wrong with just doing spin_lock/spin_unlock?

Paul.


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