Hi Russell & Linus,

Sorry for being late to reply.

On 8/14/2011 2:06 PM, Russell King - ARM Linux wrote:

On Fri, Jul 29, 2011 at 04:19:26PM +0530, Viresh Kumar wrote:

quoted

Untill now, sg_len greater than one is not supported. This patch adds support to
do that.

I'm not sure that this is the correct approach.  memcpy()s can only be
used with one single buffer, so the sg stuff for that (and the unmapping
support) doesn't make sense at all.

I am not sure if i get this completely. In memcpy, we still don't support
more than one sg. We have created a new member in txd, which keeps track of
data (addresses, len).

While unmapping, we are unmapping only single dsg. I think i don't need to
use list_for_each_entry() there, as there is only one element present in list.
But can still keep that.

The only place where this makes sense is the slave sg stuff.  I wonder
whether we can better deal with that by having the LLI setup code deal
with one SG list entry at a time, and chain each together.

Something I've also been pondering which is related to this is linking
together DMA operations using the LLI chaining when interrupts and
callbacks aren't required.  It's a very similar problem.  Other DMA
engine drivers do this.

Are you talking about linking all sg's together or linking multiple calls to
prep_dma_memcpy? I am handling the first.

Finally, note that some of the PL08x code assumes that for any TXD,
the LLI list is a contiguous array.  See the first part of
pl08x_getbytes_chan(). That needs fixing as soon as we start going to
more than one SG list entry.

We still have one contiguous array for LLI list. In pl08x_fill_llis_for_desc()
i am using same txd->llis_va for all sg's.

Sorry if i misunderstood your concerns.

-- 
viresh