Laxman Dewangan wrote at Wednesday, January 25, 2012 6:46 PM:

On Wednesday 25 January 2012 10:33 PM, Stephen Warren wrote:

quoted

Laxman Dewangan wrote at Wednesday, January 25, 2012 4:20 AM:

quoted

Allow the transfer size to vary in each DMA request,
rather than assuming all requests to be the same size
as the first request made.

...

quoted

diff --git a/arch/arm/mach-tegra/dma.c b/arch/arm/mach-tegra/dma.c

...

quoted

@@ -434,6 +435,15 @@ static void tegra_dma_update_hw_partial(struct tegra_dma_channel *ch,
  	writel(apb_ptr, ch->addr + APB_DMA_CHAN_APB_PTR);
  	writel(ahb_ptr, ch->addr + APB_DMA_CHAN_AHB_PTR);

+	if (ch->mode&  TEGRA_DMA_MODE_CONTINOUS)
+		ch->req_transfer_count = (req->size>>  3) - 1;
+	else
+		ch->req_transfer_count = (req->size>>  2) - 1;

There are cases in the current continuous mode where HW is working on
one buffer and the next buffer is queued in HW. Once we've written the
new request to HW, we don't know exactly which buffer HW is operating
on. Hence, we don't know which buffer ch->req_transfer_count refers to.
If req->size changes, might this change cause the new req->size value
to be used when the old buffer's final completion interrupt goes off
and hence the old buffer's req->bytes_transferred be wrong?

Then byte_transferred should be calculated based on req->size, not based
on ch->req_transfer_count.

Yes, I think that makes sense.

Still issue may come when we need to read the transfered count from dma
through status register whether it has completed the old and started new
one or still on old req. This can be resolved by having proper lock
between the isr and reading status so that if isr clears the
interrupt_done, just raise a flag that int_done arrive and so
get-active_count() function can handle it properly before workqueu get
scheduled. I am seeing that there is  missing synchronization between
int_done status and get_active_count().
I am also thinking that we can remove the work queue and handle the
queue management in isr only

So I assume you need to make some/all of those modifications before we can
apply this patch?

quoted

Actually looking at the current continuous mode, I'm not convinced that
it correctly handles replacing an in-progress buffer with a new buffer;
I certainly see where handle_continuous_dma() checks for a second (SW)
queued buffer and tells the HW to use that buffer instead, but I don't
see where the (SW) queue management is done; where is the old req removed
from the head of ch->list and marked complete? I assume the "out of sync"
case is only intended to be an error condition and not part of the
buffer switch?

We are removing the old req from list in handling of full buffer
interrupt handling.

660                 } else if (req->buffer_status ==
661                         TEGRA_DMA_REQ_BUF_STATUS_HALF_FULL) {
:::::::::::::::::::::::::::::::::::::::
670                         req->buffer_status =
TEGRA_DMA_REQ_BUF_STATUS_FULL;
671                         req->bytes_transferred = bytes_transferred;
672                         req->status = TEGRA_DMA_REQ_SUCCESS;
673                         list_del(&req->node);

Oh right... Maybe I'm misunderstanding continuous mode works then; I
thought that the client driver queued a request once, and it continued
to execute forever until either a new request was queued to replace it,
or the original request for dequeued. It looks like instead, the req
is always removed from the queue once we've seen both the ping and the
pong interrupts. Am I totally misunderstanding what's happening?

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