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Subject[PATCH] Revert "dmaengine: pl330: add DMA_PAUSE feature"
Date
This reverts commit 88987d2c7534a0269f567fb101e6d71a08f0f01d.

The pl330.c pause implementation violates the dmaengine requirement
for no data loss, since it relies on the DMAKILL
instruction. However, DMAKILL discards in-flight data from the
dma controller's fifo. This is documented in the dma-330 manual
and I have observed it with hardware doing device-to-memory burst
transfers. The discarded data may or may not show up in the
residue count, depending on timing (resulting in data corruption
effectively).

Signed-off-by: Frank Mori Hess <fmh6jj@gmail.com>
---
drivers/dma/pl330.c | 28 ----------------------------
1 file changed, 28 deletions(-)

diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
index 6237069001c4..f802bd3b0481 100644
--- a/drivers/dma/pl330.c
+++ b/drivers/dma/pl330.c
@@ -2290,33 +2290,6 @@ static int pl330_terminate_all(struct dma_chan *chan)
return 0;
}

-/*
- * We don't support DMA_RESUME command because of hardware
- * limitations, so after pausing the channel we cannot restore
- * it to active state. We have to terminate channel and setup
- * DMA transfer again. This pause feature was implemented to
- * allow safely read residue before channel termination.
- */
-static int pl330_pause(struct dma_chan *chan)
-{
- struct dma_pl330_chan *pch = to_pchan(chan);
- struct pl330_dmac *pl330 = pch->dmac;
- unsigned long flags;
-
- pm_runtime_get_sync(pl330->ddma.dev);
- spin_lock_irqsave(&pch->lock, flags);
-
- spin_lock(&pl330->lock);
- _stop(pch->thread);
- spin_unlock(&pl330->lock);
-
- spin_unlock_irqrestore(&pch->lock, flags);
- pm_runtime_mark_last_busy(pl330->ddma.dev);
- pm_runtime_put_autosuspend(pl330->ddma.dev);
-
- return 0;
-}
-
static void pl330_free_chan_resources(struct dma_chan *chan)
{
struct dma_pl330_chan *pch = to_pchan(chan);
@@ -3027,7 +3000,6 @@ pl330_probe(struct amba_device *adev, const struct amba_id *id)
pd->device_tx_status = pl330_tx_status;
pd->device_prep_slave_sg = pl330_prep_slave_sg;
pd->device_config = pl330_config;
- pd->device_pause = pl330_pause;
pd->device_terminate_all = pl330_terminate_all;
pd->device_issue_pending = pl330_issue_pending;
pd->src_addr_widths = PL330_DMA_BUSWIDTHS;
--
2.11.0

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