Just some corrections here..

On 08/01/2013 03:28 PM, Joel Fernandes wrote:

quoted

quoted

2. If the interrupt handler for some reason doesn't complete or get
service in time, we will end up DMA'ing incorrect data as events
wouldn't stop coming in even if interrupt is not yet handled (in your
example linked sets P1 or P2 would be old ones being repeated). Where as
with my method, we are not doing any DMA once we finish the current
MAX_NR_SG set even if events continue to come.

Where is repetition and possibility of wrong data being transferred? We
have a linear list of PaRAM sets - not a loop. You would link the end to
PaRAM set chain to dummy PaRAM set which BTW will not cause missed
events. The more number of PaRAM sets you add to the chain, the more

There would have to be a loop, how else would you ensure continuity and
uninterrupted DMA?

Consider if you have 2 sets of linked sets:
L1 is the first set of Linked sets and L2 is the second.

When L1 is done, EDMA continues with L2 (due to the link) while
interrupt handler prepares L1. The continuity depends on L1 being linked
to L2. Only the absolute last break up of the MAX_NR_SG linked set will
be linked to Dummy.

So consider MAX_NR_SG=10, and sg_len = 35

L1 - L2 - L1 - L1 - Dummy

Should be,
L1 - L2 - L1 - L2 - Dummy

The split would be in number of slots,
10 - 10 - 10 -  5 - Dummy

quoted

time CPU gets to intervene before DMA eventually stalls. This is a
tradeoff system designers can manage.

Consider what happens in the case where MAX_SG_NR=1 or 2. In that case,
there's a change we might not get enough time for the interrupt handler
to setup next series of linked set.

Some how this limitation has to be overcome by advising in comments than
MAX_SG_NR should always be greater than a certain number to ensure
proper operation.

s/than/that/


Thanks,

-Joel