linux-kernel - [PATCH v3 2/4] dmaengine: xilinx_vdma: Simplify spin lock handling

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Message-ID: <1456495434-11722-2-git-send-email-appanad@xilinx.com>
Date:	Fri, 26 Feb 2016 19:33:52 +0530
From:	Kedareswara rao Appana <appana.durga.rao@...inx.com>
To:	<dan.j.williams@...el.com>, <vinod.koul@...el.com>,
	<michal.simek@...inx.com>, <soren.brinkmann@...inx.com>,
	<appanad@...inx.com>, <moritz.fischer@...us.com>,
	<laurent.pinchart@...asonboard.com>, <luis@...ethencourt.com>,
	<anirudh@...inx.com>
CC:	<dmaengine@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH v3 2/4] dmaengine: xilinx_vdma: Simplify spin lock handling

This patch simplifies the spin lock handling in the driver
by moving locking out of xilinx_dma_start_transfer() API
and xilinx_dma_update_completed_cookie() API.

Signed-off-by: Kedareswara rao Appana <appanad@...inx.com>
---
Changes for v3:
---> Updated commit message as suggested by vinod.
---> Added description to the API's(start_transfer/complete_cookie) regarding
locking as suggested by vinod.
Changes for v2:
---> splitted the changes into multiple patches

 drivers/dma/xilinx/xilinx_vdma.c | 29 ++++++++++++-----------------
 1 file changed, 12 insertions(+), 17 deletions(-)

diff --git a/drivers/dma/xilinx/xilinx_vdma.c b/drivers/dma/xilinx/xilinx_vdma.c
index 06bffec..ce330d4 100644
--- a/drivers/dma/xilinx/xilinx_vdma.c
+++ b/drivers/dma/xilinx/xilinx_vdma.c
@@ -605,17 +605,15 @@ static void xilinx_vdma_start_transfer(struct xilinx_vdma_chan *chan)
 {
 	struct xilinx_vdma_config *config = &chan->config;
 	struct xilinx_vdma_tx_descriptor *desc, *tail_desc;
-	unsigned long flags;
 	u32 reg;
 	struct xilinx_vdma_tx_segment *tail_segment;
 
+	/* This function was invoked with lock held */
 	if (chan->err)
 		return;
 
-	spin_lock_irqsave(&chan->lock, flags);
-
 	if (list_empty(&chan->pending_list))
-		goto out_unlock;
+		return;
 
 	desc = list_first_entry(&chan->pending_list,
 				struct xilinx_vdma_tx_descriptor, node);
@@ -629,7 +627,7 @@ static void xilinx_vdma_start_transfer(struct xilinx_vdma_chan *chan)
 	if (chan->has_sg && xilinx_vdma_is_running(chan) &&
 	    !xilinx_vdma_is_idle(chan)) {
 		dev_dbg(chan->dev, "DMA controller still busy\n");
-		goto out_unlock;
+		return;
 	}
 
 	/*
@@ -676,7 +674,7 @@ static void xilinx_vdma_start_transfer(struct xilinx_vdma_chan *chan)
 	xilinx_vdma_start(chan);
 
 	if (chan->err)
-		goto out_unlock;
+		return;
 
 	/* Start the transfer */
 	if (chan->has_sg) {
@@ -696,7 +694,7 @@ static void xilinx_vdma_start_transfer(struct xilinx_vdma_chan *chan)
 		}
 
 		if (!last)
-			goto out_unlock;
+			return;
 
 		/* HW expects these parameters to be same for one transaction */
 		vdma_desc_write(chan, XILINX_VDMA_REG_HSIZE, last->hw.hsize);
@@ -707,9 +705,6 @@ static void xilinx_vdma_start_transfer(struct xilinx_vdma_chan *chan)
 
 	list_splice_tail_init(&chan->pending_list, &chan->active_list);
 	chan->desc_pendingcount = 0;
-
-out_unlock:
-	spin_unlock_irqrestore(&chan->lock, flags);
 }
 
 /**
@@ -719,8 +714,11 @@ out_unlock:
 static void xilinx_vdma_issue_pending(struct dma_chan *dchan)
 {
 	struct xilinx_vdma_chan *chan = to_xilinx_chan(dchan);
+	unsigned long flags;
 
+	spin_lock_irqsave(&chan->lock, flags);
 	xilinx_vdma_start_transfer(chan);
+	spin_unlock_irqrestore(&chan->lock, flags);
 }
 
 /**
@@ -732,21 +730,16 @@ static void xilinx_vdma_issue_pending(struct dma_chan *dchan)
 static void xilinx_vdma_complete_descriptor(struct xilinx_vdma_chan *chan)
 {
 	struct xilinx_vdma_tx_descriptor *desc, *next;
-	unsigned long flags;
-
-	spin_lock_irqsave(&chan->lock, flags);
 
+	/* This function was invoked with lock held */
 	if (list_empty(&chan->active_list))
-		goto out_unlock;
+		return;
 
 	list_for_each_entry_safe(desc, next, &chan->active_list, node) {
 		list_del(&desc->node);
 		dma_cookie_complete(&desc->async_tx);
 		list_add_tail(&desc->node, &chan->done_list);
 	}
-
-out_unlock:
-	spin_unlock_irqrestore(&chan->lock, flags);
 }
 
 /**
@@ -857,8 +850,10 @@ static irqreturn_t xilinx_vdma_irq_handler(int irq, void *data)
 	}
 
 	if (status & XILINX_VDMA_DMASR_FRM_CNT_IRQ) {
+		spin_lock(&chan->lock);
 		xilinx_vdma_complete_descriptor(chan);
 		xilinx_vdma_start_transfer(chan);
+		spin_unlock(&chan->lock);
 	}
 
 	tasklet_schedule(&chan->tasklet);
-- 
2.1.2