Messages in this thread | | | Date | Thu, 18 Aug 2011 14:08:19 +0530 | From | Viresh Kumar <> | Subject | Re: [PATCH 16/18] dmaengine/amba-pl08x: Add support for sg len greater than one for slave transfers |
| |
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: >> 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
| |