linux-kernel - Re: 2.6.26-rc1 regression: ISA DMA broken (bisected)

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Message-Id: <200805131718.40138.bjorn.helgaas@hp.com>
Date:	Tue, 13 May 2008 17:18:39 -0600
From:	Bjorn Helgaas <bjorn.helgaas@...com>
To:	Rene Herman <rene.herman@...access.nl>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, Takashi Iwai <tiwai@...e.de>,
	Glauber Costa <gcosta@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Pete Clements <clem@...m.clem-digital.net>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	ALSA devel <alsa-devel@...a-project.org>
Subject: Re: 2.6.26-rc1 regression: ISA DMA broken (bisected)

On Tuesday 13 May 2008 11:33:25 am Rene Herman wrote:
> On 13-05-08 19:01, Alan Cox wrote:
> > On Tue, 13 May 2008 10:59:32 -0600, Bjorn Helgaas <bjorn.helgaas@...com> wrote:
> >> On Friday 09 May 2008 12:06:55 am Takashi Iwai wrote:
> >>> Thanks for catching it.  Yeah, the patch looks buggy.  We had an
> >>> implicit assumption that dev = NULL for ISA devices that require 24bit
> >>> DMA.
> >> Naive question #1:  Why don't we have a struct device for these
> >> ISA devices?  PNP builds a struct device with DMA_24BIT_MASK
> >> for ISAPNP devices.
> > 
> > Because nobody has done the needed work to get all the old ISA drivers
> > converted. I guess isa_device would actually be a platform_device
> > wrapper ?
> 
> No, isa_device is its own thing, on its own isa_bus (*). It has a struct 
> device * readily available though...
> 
> (*) drivers/base/isa.c, and explanatory changelog at:
> 
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=a5117ba7da37deb09df5eb802dace229b3fb1e9f

Thanks for the nice changelog.

isa_register_driver() currently doesn't set a DMA mask.  Should it?

I only see about 35 dma_alloc_coherent() calls that pass NULL.  I
guess even those would be a fair amount of work to change, and I
suppose there would be more that I missed.

Bjorn
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