Re: [PATCH 11/14] libata: add qc->dma_nbytes

[Jeff Garzik <jeff@garzik.org>]

Tejun Heo wrote:
> qc->nbytes doesn't include extra buffers setup by libata core layer
> and my be odd.  This patch adds qc->dma_nbytes which includes any
> extra buffers setup by libata core layer and is guaranteed to be
> aligned on 4 byte boundary.
> 
> This value is to be used to program the host controller.  As this
> represents the actual length of buffer available to the controller and
> the controller must be able to deal with short transfers for ATAPI
> commands which can transfer variable length, this shouldn't break any
> controllers while making problems like rounding-down and controllers
> choking up on odd transfer bytes much less likely.
> 
> Signed-off-by: Tejun Heo <htejun@gmail.com>
> ---
>  drivers/ata/libata-core.c       |   11 +++++++----
>  drivers/ata/pata_pdc202xx_old.c |    2 +-
>  drivers/ata/sata_inic162x.c     |    2 +-
>  drivers/ata/sata_qstor.c        |    2 +-
>  include/linux/libata.h          |    3 ++-
>  5 files changed, 12 insertions(+), 8 deletions(-)

I would suggest two values:

qc->nbytes	-> value to program host controllers with
qc->raw_nbytes	-> the precise value, without any padding etc.

IMO this makes it more likely that people will use the "right" value