[PATCH v3 RESEND] dma-mapping: add new API for max_segment_number

On 17 June 2011 14:40, Matthew Wilcox [off-list ref] wrote:

On Thu, Jun 16, 2011 at 08:30:53PM +0800, Shawn Guo wrote:

quoted

Here is the user story that tells the need of the new api. ?The
mxs-mmc is the mmc host controller for Freescale MXS architecture.
There are a pair of ?mmc host specific parameters max_seg_size and
max_segs that mxs-mmc host driver needs to tell mmc core, so that
mmc core can know how big each data segment could be and how many
segments could be handled one time in a scatter list by host driver.

The mxs-mmc driver is one user of dmaengine mxs-dma, and it will call
mxs-dma to transfer data in scatter list. ?That is to say mxs-mmc has
no idea of what max_seg_size and max_segs should be, because they are
all mxs-dma capability parameters, and mxs-mmc needs to query them
from mxs-dma.

This approach would make sense if mxs-mmc were generic, but it's tied to
mxs-dma, so it can just as well call mxs-dma to find out how many segments
it supports.

mxs-dma use the generic dmaengine.h. The patch is not only intended
for mxs-mmc. MMCI and other mmc host drivers need a way to query
max_seg_number.
It would be possible to store this number within drivers/dmaengine but
this would not work for omap_hsmmc that doesn't use drivers/dmaengine

Regards,
Per