linux-kernel - Re: sata_nv + ADMA + Samsung disk problem

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Date:	Thu, 03 Jan 2008 19:43:39 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	benh@...nel.crashing.org
Cc:	Mark Lord <liml@....ca>, Allen Martin <AMartin@...dia.com>,
	Jeff Garzik <jeff@...zik.org>, Tejun Heo <htejun@...il.com>,
	Gabor Gombas <gombasg@...aki.hu>, linux-kernel@...r.kernel.org,
	linux-ide@...r.kernel.org, Kuan Luo <kluo@...dia.com>,
	Peer Chen <pchen@...dia.com>
Subject: Re: sata_nv + ADMA + Samsung disk problem

Benjamin Herrenschmidt wrote:
>> Another thing about the PacDigi core:  one has to be very careful
>> to avoid sequential accesses to sequential PCI locations when
>> programming the chip -- it cannot handle merged register writes.
>>
>> So for any group of sequentially laid out registers, the code has
>> to ensure it never writes two adjacent registers in sequence..
> 
> Ugh ? Write combining isn't permitted on normal registers afaik...
> 
> Ben.

Byte merging can be done by the chipset on MMIO writes (merging multiple 
8 or 16-bit writes into a single 32-bit cycle).
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