[PATCH 1/3] dmaengine: pl330: Set residue in tx_status callback.

[Dylan Reid]

On Sun, Oct 6, 2013 at 8:48 PM, Vinod Koul <vinod.koul at intel.com> wrote:
> On Mon, Oct 07, 2013 at 10:39:34AM +0900, Chanho Park wrote:
>> > > Why didn't you use a cookie value to track the request?
>> > > The cookie is assigned when each transfer is submitted.
>> > > If you save the value in the desc, we can find the request easily.
>> >
>> > If there are several cyclic desc in the work list, is there a better way
>> > to find the "current" one?  The chan struct tracks the last completed and
>> > last submitted cookies, but these will be the first and last
>> > respectively as long as the cyclic transfer is active.  Is there an
>> > "active" cookie stored somewhere that I missed?
>>
>> Assume there are three cookies. If you want to get the second cookie not
>> latest cookie, your way can be also correct in such case?
>> I think tx_status API is to get dma status of the given cookie.
>> You are only considering a cyclic case.
> For cyclic case you would have possible same descriptor running till you
> terminate.

The cyclic case that makes this interesting is when there are multiple
cyclic descriptors in the list. The cookie and completed_cookie
markers don't help to determine which of the descriptors in the list
is currently active.  dma_cookie_complete isn't called for a cyclic
desc, the desc is just pushed to the end of the list.

>
> For non cyclic, if you have 3 descriptors submitted, the cookie value can be, say
> 7, 8 and 9. If you query the status of any descriptor and pass the last optional
> txstate arg then you will know the last cookie completed. so if txstate->last is
> 7, then 7th was completed and 8 should be running and 9 in queue!

Got it, but the correct desc for cookie 8 will still have to be
searched for, correct?

Thanks for the advise.

Dylan

>> > Looking for the first buffer with status == BUSY is an improvement I'll
>> > make.  Any way to avoid looking through the list?
> Its already there :)
>
> --
> ~Vinod