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Re: cache coherency in DMA and MMIO

From: Da Zheng
Subject: Re: cache coherency in DMA and MMIO
Date: Sat, 24 Apr 2010 18:29:50 +0800
User-agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv: Gecko/20100317 Thunderbird/3.0.4

On 10-4-23 下午7:37, Samuel Thibault wrote:
> Da Zheng, le Fri 23 Apr 2010 14:51:22 +0800, a écrit :
>> They are not just one or two variables. They are an array of structure
>> variables. Should I define all fields of the structure with volatile 
>> qualifier?
> You can qualify the whole structure
>> It's strange. The Linux driver doesn't do so but it definitely works in the
>> Linux kernel.
> It does (or should do): such pointers have the __io qualifier.
I checked the code of e1000 again. The data for MMIO is qualified by __iomem,
but the data in the transmission or receiving queues (which are accessed by DMA)
doesn't have __iomem or any similar qualifiers. I guess the data in the
transmission queue is very unlikely to be in registers when the driver accesses 

Zheng Da

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