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Message-ID: <17182.32625.930500.874251@cargo.ozlabs.ibm.com>
Date: Wed, 7 Sep 2005 15:49:37 +1000
From: Paul Mackerras <paulus@samba.org>
To: Grant Grundler <grundler@parisc-linux.org>
Cc: Brian King <brking@us.ibm.com>, Andrew Morton <akpm@osdl.org>,
       greg@kroah.com, matthew@wil.cx, benh@kernel.crashing.org, ak@muc.de,
       linux-kernel@vger.kernel.org, alan@lxorguk.ukuu.org.uk,
       linux-pci@atrey.karlin.mff.cuni.cz
Subject: Re: [PATCH 1/2] pci: Block config access during BIST (resend)
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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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