linux-kernel - Re: SATA_SIL on IXP425 workaround

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Message-ID: <4B51489F.8010105@gmail.com>
Date:	Fri, 15 Jan 2010 23:03:27 -0600
From:	Robert Hancock <hancockrwd@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Krzysztof Halasa <khc@...waw.pl>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	linux-ide@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>
Subject: Re: SATA_SIL on IXP425 workaround

On 01/14/2010 03:05 PM, Alan Cox wrote:
>> We need to use the MMIO BAR at least for starting DMA transfers, the
>> I/O ones are 64KB-limited. We can't just use read[bw] if reading all
>> 32 bits has side effects.
>
> Last time I instrumented this on x86 we never issued a>  64K linear block
> in our s/g lists. In fact we went for years before anyone noticed we had
> a bug with CS5530 and a couple of other chips that mishandled 64K segment
> sizes, and that was only finally noticed in a very specific and weird
> circumstance.

Having a block over 64KB may be rare, but the other thing that the large 
block transfer feature does is remove the restriction on a block 
crossing a 64KB boundary, which based on the experiments I did when I 
worked on adding the feature, does happen fairly commonly if the driver 
allows it.
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