Date: Wed, 27 Feb 2008 00:02:22 +0000
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Jeff Garzik <jgarzik@pobox.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Ingo Molnar <mingo@elte.hu>,
       Thomas Gleixner <tglx@linutronix.de>,
       =?UTF-8?B?QmrDtnJu?= Steinbrink <B.Steinbrink@gmx.de>,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: 2.6.24-git: kmap_atomic() WARN_ON()
Message-ID: <20080227000222.158f9220@core>
In-Reply-To: <47C499CF.2000605@pobox.com>
References: <alpine.LFD.1.00.0802070054220.9204@apollo.tec.linutronix.de>
	<20080225195924.GA23176@atjola.homenet>
	<47C32043.6090809@pobox.com>
	<20080225124054.9b69e9f0.akpm@linux-foundation.org>
	<alpine.LFD.1.00.0802252242290.7583@apollo.tec.linutronix.de>
	<47C34CEA.7060307@pobox.com>
	<20080226083904.GC9857@elte.hu>
	<47C43F18.6060207@pobox.com>
	<20080226101928.f6c16c66.akpm@linux-foundation.org>
	<20080226204943.GD14350@elte.hu>
	<20080226133715.d9cd32e7.akpm@linux-foundation.org>
	<47C499CF.2000605@pobox.com>
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> Aside: The "FIXME: use bounce buffer" comment above indicates the more 
> optimal PIO data xfer approach of
> 
> 	local_irq_save()
> 	kmap_atomic()
> 	memcpy into bounce buffer
> 	kunmap_atomic()
> 	local_irq_restore()
> 
> 	/* do slow PIO bitbanging data transfer */
> 	ap->ops->data_xfer(...)

Definitely - older PATA controllers are unbuffered. A PIO_0 transfer is
running at ISA speed with IRQs off. Guaranteed to give Ingo's RT a blip.

Alan
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