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

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Message-ID: <s5hod79avks.wl%tiwai@suse.de>
Date:	Wed, 14 May 2008 15:01:23 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Rene Herman <rene.herman@...access.nl>
Cc:	Bjorn Helgaas <bjorn.helgaas@...com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	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)

At Wed, 14 May 2008 14:46:44 +0200,
Rene Herman wrote:
> 
> On 14-05-08 01:18, Bjorn Helgaas wrote:
> 
> > On Tuesday 13 May 2008 11:33:25 am Rene Herman wrote:
> 
> >> 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?
> 
> If it's going to be useful, definitely. The attached does not just set
> 
>    dev->dma_mask = &dev->coherent_dma_mask
> 
> as in the fallback_dev when dma_alloc_coherent() is passed a NULL device 
> only due to the mask juggling in snd_dma_hack_alloc_coherent() (which 
> wouldn't break, but...) but introduces its own copy in struct isa_dev 
> same as struct pnp_dev. As far as I'm aware, there's no actual reason 
> for keeping it other than that and if the hack could go I'd rather lose 
> the private mask copy again also.

The snd_dma_hack_alloc_coherent() is gone in the latest ALSA tree.
It wasn't merged to 2.6.26, though.


> (the device model still uses a plain u64 by the way but I guess the 
> clean type would be a dma64_addr_t)
> 
> Inlining is whitespace-failing here. Patch itself is trivial...
> 
> > 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.
> 
> At least the ALSA one isn't passing a literal NULL it seems. But yes, 
> current NULL-hack reinstatement (it's been merged by Linus already) is 
> definitely the correct fix for now.

Yes.  We need to fix the caller of snd_pcm_lib_preallocate_pages*()
under sound/isa.  Currently it's called with snd_dma_isa_data(), which
is expanded to NULL.  Replace it with a proper device pointer should
suffice.


Takashi
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