On 30.06.2016 17:15, Niklas Söderlund wrote:
From: Muhammad Hamza Farooq <mfarooq@xxxxxxxxxxx>
The hardware might have complete the transfer but the interrupt handler
might not have had a chance to run. If rcar_dmac_chan_get_residue()
which reads HW registers finds that there is no residue return
DMA_COMPLETE.
Signed-off-by: Muhammad Hamza Farooq <mfarooq@xxxxxxxxxxx>
Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
[Niklas: add explanation in commit message]
Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@xxxxxxxxxxxx>
Acked-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
---
drivers/dma/sh/rcar-dmac.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
index dfb1792..791a064 100644
--- a/drivers/dma/sh/rcar-dmac.c
+++ b/drivers/dma/sh/rcar-dmac.c
@@ -1202,6 +1202,10 @@ static enum dma_status rcar_dmac_tx_status(struct dma_chan *chan,
residue = rcar_dmac_chan_get_residue(rchan, cookie);
spin_unlock_irqrestore(&rchan->lock, flags);
+ /* if there's no residue, the cookie is complete */
+ if (!residue)
+ return DMA_COMPLETE;
+
dma_set_residue(txstate, residue);
return status;
We have some doubts about this change (mainline commit [1]). Not being a
DMA expert, let me try to explain:
We are configuring a cyclic, never ending DMA
(dmaengine_prep_dma_cyclic()). For this cyclic DMA we continuously poll
the residue (txstate->residue) via rcar_dmac_tx_status(). Having a
cyclic, never ending DMA we think that residue == 0 is a valid value.
However, with above change, a residue value of 0 is 'dropped' and never
written via dma_set_residue() to txstate. So in case we continuously
poll, this value is lost, resulting in wrong behavior of the caller.
In our case with cyclic, never ending DMA, changing this to
--- a/drivers/dma/sh/rcar-dmac.c
+++ b/drivers/dma/sh/rcar-dmac.c
@@ -1388,7 +1388,7 @@ static enum dma_status rcar_dmac_tx_status(struct
dma_chan *chan,
/* if there's no residue, the cookie is complete */
if (!residue)
- return DMA_COMPLETE;
+ status = DMA_COMPLETE;
dma_set_residue(txstate, residue);
seems to help. If we ignore the still wrong DMA_COMPLETE status (which
in case of cyclic DMA doesn't make any sense?) the caller get the
correct txstate->residue values (not dropping the 0).
So maybe we need anything like
--- a/drivers/dma/sh/rcar-dmac.c
+++ b/drivers/dma/sh/rcar-dmac.c
@@ -1387,7 +1387,7 @@ static enum dma_status rcar_dmac_tx_status(struct
dma_chan *chan,
spin_unlock_irqrestore(&rchan->lock, flags);
/* if there's no residue, the cookie is complete */
- if (!residue)
+ if (!residue && !chan->desc.running->cyclic)
return DMA_COMPLETE;
dma_set_residue(txstate, residue);
?
Opinions?
Best regards
Dirk
[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/dma/sh/rcar-dmac.c?h=v5.0-rc2&id=3544d2878817bd139dda238cdd86a15e1c03d037
