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
To email, remove "nospam" from hancockr@nospamshaw.ca
Home Page: http://www.roberthancock.com/

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