Re: Quick question about libata and hdparm

[Mark Lord <lkml@rtr.ca>]

Rogério Brito wrote:
> Dear people,
> 
> I have one small question regarding the libata drivers and the 
> interaction with hdparm.
> 
> I am presently using PATA/IDE devices only, but some distributions 
> provide kernels with libata by default (and some defconfigs also use 
> libata even for IDE devices).
> 
> Using the usual IDE drivers, I can use/query various parameters with 
> hdparm, like, for instance, the -m option, the -c option or even 
> disabling DMA. With the libata drivers, this is all that I get:
..
> Am I doing something incorrectly? I would like at least to understand 
> what is happening and, if possible, to fine-tune some settings.
..

Nearly all of the hdparm flags work fine with libata and SATA/PATA drives.
Among the *very few* that do not, are the -m and -d flags.  -c will be working
in the newest kernels, but not yet in most distro kernels.

The -d flag is not permitted by libata, as the kernel prefers to completely
dictate DMA / PIO, and it does do a rather good job of it.

The -m flag could be done, and I even have code in hdparm to do it,
but libata is very buggy with multi-sector I/O, so -m is currently is disallowed.

Cheers