linux-kernel - Re: [PATCH RFC] swiotlb: Remove SWIOTLB overflow buffer support

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Date:	Tue, 10 Jul 2012 10:55:07 -0600
From:	Shuah Khan <shuah.khan@...com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	fujita.tomonori@....ntt.co.jp, LKML <linux-kernel@...r.kernel.org>,
	akpm@...ux-foundation.org, paul.gortmaker@...driver.com,
	bhelgaas@...gle.com, amwang@...hat.com, shuahkhan@...il.com
Subject: Re: [PATCH RFC] swiotlb: Remove SWIOTLB overflow buffer support

On Mon, 2012-07-09 at 16:25 -0400, Konrad Rzeszutek Wilk wrote:
> On Fri, Jul 06, 2012 at 05:06:12PM -0600, Shuah Khan wrote:
> > Remove SWIOTLB overflow buffer support and return DMA_ERROR_CODE
> > (a value of zero) to make it consistent with iommu implementation
> > on Intel, AMD, and swiotlb-xen.
> 
> While this is a good forward step and this needs to be done eventually,
> you should first send out patches for the drivers that don't check
> for the DMA_ERROR_CODE when doing mapping. In other words for the
> drivers that map but don't call dma_mapping_error to check.
> 
> When that is fixed and *all the drivers that don't call dma_mapping_error
> are fixed, then this patch makes sense.

The challenge will be catching all the drivers and have confidence that
all of them are covered. I will start looking into this to get a feel
for how many drivers needs fixing.

Also, isn't this problem today with other iommu implementations? All of
the other iommu implementation don't have support for overflow buffers?

-- Shuah



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