linux-kernel - [PATCH v4 2/2] dma: pl330: add DMA

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Date:	Wed, 11 Feb 2015 13:23:18 +0100
From:	Robert Baldyga <r.baldyga@...sung.com>
To:	vinod.koul@...el.com
Cc:	dan.j.williams@...el.com, lars@...afoo.de,
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
	m.szyprowski@...sung.com, k.kozlowski@...sung.com,
	Robert Baldyga <r.baldyga@...sung.com>
Subject: [PATCH v4 2/2] dma: pl330: add DMA_PAUSE feature

DMA_PAUSE command is used for halting DMA transfer on chosen channel.
It can be useful when we want to safely read residue before terminating
all requests on channel. Otherwise there can be situation when some data
is transferred before channel termination but after reading residue,
which obviously results with data loss. To avoid this situation we can
pause channel, read residue and then terminate all requests.
This scenario is common, for example, in serial port drivers.

Signed-off-by: Robert Baldyga <r.baldyga@...sung.com>
---
 drivers/dma/pl330.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
index 517abd6..3c2fcd6 100644
--- a/drivers/dma/pl330.c
+++ b/drivers/dma/pl330.c
@@ -2149,6 +2149,33 @@ 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.
+ */
+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);
@@ -2836,6 +2863,7 @@ 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;
-- 
1.9.1

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