Date: Tue, 1 Feb 2011 14:22:01 +0900
To: hancockrwd@gmail.com
Cc: fujita.tomonori@lab.ntt.co.jp, ak@linux.intel.com, cebbert@redhat.com,
        linux-kernel@vger.kernel.org, dwmw2@infradead.org
Subject: Re: b44 driver causes panic when using swiotlb
From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
In-Reply-To: <4D477C6F.8000906@gmail.com>
References: <4D4759BD.2000006@gmail.com>
	<20110201102707C.fujita.tomonori@lab.ntt.co.jp>
	<4D477C6F.8000906@gmail.com>
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On Mon, 31 Jan 2011 21:22:23 -0600
Robert Hancock <hancockrwd@gmail.com> wrote:

> > Some ideas to implement something that works for such device were
> > discussed. Seems that the conclusion is that it's doesn't worth making
> > the common code complicated for such minor and insane devices.
> 
> I don't think this is the only device that has sub-32-bit DMA 
> restrictions, this will just lead to a bunch of duplicated code.

Yeah, not only device but not many.

The block layer has the own bouncing mechanism. Some network drivers
have the similar bouncing code. I don't know if there are other kinds
of drivers that have the own bouncing code.

I thought that we can make mm/bounce.c (used for block drivers now)
work any drivers without complicating it. We could make swiotlb to do
but it's too complicated and it doesn't worth.


> In 
> particular, how is LPC DMA supposed to work?

LPC DMA can't do 32bit dma?


> At the very least we should be allowing the driver to deal with the 
> failure instead of panicing the system. Otherwise we are just leaving a 
> land mine for people to trip over.

Agreed. swiotlb shouldn't panic in this case. I'll take care of it.
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