Re: [PATCH] drivers/ata: Add the SW NCQ support to sata_nv for MCP51/MCP55/MCP61

[Robert Hancock <hancockr@shaw.ca>]

Zoltan Boszormenyi wrote:
> Hi,
> 
> thanks for publishing this.
> 
>> Add the Software NCQ support to sata_nv.c for MCP51/MCP55/MCP61 SATA
>> controller.
>>
>> This patch base on sata_nv.c file from kernel 2.6.22-rc1
>>
>> See attachment for the patch.
>>
>> Signed-off-by: Kuan Luo <kluo@nvidia.com>
>> Signed-off-by: Peer Chen <pchen@nvidia.com>
>> ==================================
>> See attached file.
>> ==================================
>>   
> 
> However, I saw this in the patch:
> 
> +               /* determine if physical DMA addr spans 64K boundary.
> +                * Note h/w doesn't support 64-bit, so we unconditionally
> +                * truncate dma_addr_t to u32.
> +                */
> +               addr = (u32) sg_dma_address(sg);
> 
> Does it mean that I can't upgrade my machine to 4 GB or more
> without losing NCQ or risking data corruption?
> Can the code be made IOMMU-aware?

That shouldn't be a problem, libata default DMA mask is 32 bits (which 
isn't overridden with this controller) and so the block layer will 
bounce any data being read/written above that point with IOMMU or 
swiotlb. The comment is a bit unnecessarily scary.

-- 
Robert Hancock      Saskatoon, SK, Canada
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