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Date: Wed, 12 Apr 2006 22:05:34 -0700
From: Andrew Morton <akpm@osdl.org>
To: Seokmann.Ju@lsil.com, Seokmann.Ju@engenio.com,
       James.Bottomley@SteelEye.com, linux-kernel@vger.kernel.org,
       linux-scsi@vger.kernel.org
Subject: Re: [PATCH 1/1] megaraid_{mm,mbox}: fix a bug in reset handler
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Andrew Morton <akpm@osdl.org> wrote:
>
>  > @@ -2918,12 +2933,12 @@
>  >  	wmb();
>  >  	WRINDOOR(raid_dev, raid_dev->mbox_dma | 0x1);
>  >  
>  > -	for (i = 0; i < 0xFFFFF; i++) {
>  > +	for (i = 0; i < 0xFFFFFF; i++) {
>  >  		if (mbox->numstatus != 0xFF) break;
>  >  		rmb();
>  >  	}
> 
>  Oh my.  That's an awfully long interrupts-off spin.

And if that mbox is in main memory, the duration of this spin will vary by
a factor of many tens across all the different machines on which this
driver must operate.

Careful use of ndelay() or udelay() would fix that.