[PATCH] Re: Forcing modes in libata (was: SATA buffered read VERY

[Zoltan Boszormenyi]

Hi,

Once upon a time FD Cami wrote:
> On Sun, 6 Jan 2008 13:36:09 +0000
> Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote:
>
> > On Sun, 6 Jan 2008 08:03:31 +0300
> > > > For now you can boot with libata.dma=1 to select DMA on disks but
> > > > not CD
> > > 
> > > Great, but why isn't this in the documentation?
> > 
> > Send patches
>
> patch attached.
>
> Description : Add libata.dma= to Documentation/kernel-parameters.txt
>
> Found documentation in :
> http://www.mail-archive.com/linux-ide%40vger.kernel.org/msg09849.html
> http://www.redhat.com/archives/fedora-extras-commits/2007-October/msg04568.html
>
> Signed-off-by: François Cami <francois.cami@xxxxxxx>
>
> *["libata-doc-patch.txt" (text/plain)]* <http://marc.info/?l=linux-kernel&m=119963307018562&q=p3>
>
> diff -rU2 linux-2.6.24-rc6/Documentation/kernel-parameters.txt \
>                 linux-2.6.24-rc6-mine/Documentation/kernel-parameters.txt
> --- linux-2.6.24-rc6/Documentation/kernel-parameters.txt	2008-01-06 \
>                 15:58:54.000000000 +0100
> +++ linux-2.6.24-rc6-mine/Documentation/kernel-parameters.txt	2008-01-06 \
> 16:11:20.000000000 +0100 @@ -883,4 +883,11 @@
>  			C2 power state.
>  
> +	libata.dma=	[LIBATA] DMA control
> +			libata.dma=0	  Disable all PATA DMA like old IDE
> +			libata.dma=1	  Disk DMA only
> +			libata.dma=2	  ATAPI DMA only
> +			libata.dma=3	  CF DMA only 
> +			libata.dma=0,1,3  Combinations also work.
> +
>   

The code patch you are looking at has little different semantics.
(1 << 2) is 4 not 3... Values for different devices are:

1  - ATA
2 - ATAPI
4 - CF

The parameter is a bitmask of 1, 2, 4. Default is 7.
2.6.24-rc3 also has this in libata-core.c which confirms
the acceptance of a bitmask :

static int libata_dma_mask = 
ATA_DMA_MASK_ATA|ATA_DMA_MASK_ATAPI|ATA_DMA_MASK_CFA;
module_param_named(dma, libata_dma_mask, int, 0444);
MODULE_PARM_DESC(dma, "DMA enable/disable (0x1==ATA, 0x2==ATAPI, 0x4==CF)");

Best regards,
Zoltán Böszörményi


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