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

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Message-id: <1416918346-2442-3-git-send-email-r.baldyga@samsung.com>
Date:	Tue, 25 Nov 2014 13:25:46 +0100
From:	Robert Baldyga <r.baldyga@...sung.com>
To:	vinod.koul@...el.com
Cc:	dan.j.williams@...el.com, ars@...afoo.de,
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
	m.szyprowski@...sung.com, l.czerwinski@...sung.com,
	Robert Baldyga <r.baldyga@...sung.com>
Subject: [PATCH 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 | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
index c32806d..9c64421 100644
--- a/drivers/dma/pl330.c
+++ b/drivers/dma/pl330.c
@@ -2115,6 +2115,26 @@ static int pl330_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd, unsigned
 		list_splice_tail_init(&pch->completed_list, &pl330->desc_pool);
 		spin_unlock_irqrestore(&pch->lock, flags);
 		break;
+	case DMA_PAUSE:
+		/*
+		 * 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.
+		 */
+		spin_lock_irqsave(&pch->lock, flags);
+
+		spin_lock(&pl330->lock);
+		_stop(pch->thread);
+		spin_unlock(&pl330->lock);
+
+		pch->thread->req[0].desc = NULL;
+		pch->thread->req[1].desc = NULL;
+		pch->thread->req_running = -1;
+
+		spin_unlock_irqrestore(&pch->lock, flags);
+		break;
 	case DMA_SLAVE_CONFIG:
 		slave_config = (struct dma_slave_config *)arg;
 
-- 
1.9.1

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