linux-kernel - Re: 2.6.24-git: kmap_atomic() WARN

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Date:	Wed, 27 Feb 2008 00:02:22 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Jeff Garzik <jgarzik@...ox.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Björn Steinbrink <B.Steinbrink@....de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.24-git: kmap_atomic() WARN_ON()

> 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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