RE: [PATCH v5 5/6] fsl-dma: use spin_lock_bh to instead of spin_lock_irqsave

-----Original Message-----
From: Ira W. Snyder [mailto:iws@ovro.caltech.edu]
Sent: Thursday, August 02, 2012 1:31 AM
To: Liu Qiang-B32616
Cc: linux-crypto@vger.kernel.org; linuxppc-dev@lists.ozlabs.org; linux-
kernel@vger.kernel.org; dan.j.williams@gmail.com; Vinod Koul; Tabi Timur-
B04825; herbert@gondor.hengli.com.au; Dan Williams; davem@davemloft.net
Subject: Re: [PATCH v5 5/6] fsl-dma: use spin_lock_bh to instead of
spin_lock_irqsave

On Wed, Aug 01, 2012 at 04:50:09PM +0800, qiang.liu@freescale.com wrote:

quoted

From: Qiang Liu <redacted>

- use spin_lock_bh() is the right way to use async_tx api,
dma_run_dependencies() should not be protected by spin_lock_irqsave();
- use spin_lock_bh to instead of spin_lock_irqsave for improving
performance, There is not any place to access descriptor queues in
fsl-dma ISR except its tasklet, spin_lock_bh() is more proper here.
Interrupts will be turned off and context will be save in irqsave,

there is needless to use irqsave..

quoted

This description is not very clear English. I understand it is not your
native language. Let me try to help.

"""
The use of spin_lock_irqsave() is a stronger locking mechanism than is
required throughout the driver. The minimum locking required should be
used instead.

Change all instances of spin_lock_irqsave() to spin_lock_bh(). All
manipulation of protected fields is done using tasklet context or weaker,
which makes spin_lock_bh() the correct choice.
"""

I will modify the description in v6, please check later.

Other than that,
Acked-by: Ira W. Snyder <redacted>

Thanks.

quoted

Cc: Dan Williams <redacted>
Cc: Vinod Koul <redacted>
Cc: Li Yang <redacted>
Cc: Timur Tabi <redacted>
Signed-off-by: Qiang Liu <redacted>
---
 drivers/dma/fsldma.c |   30 ++++++++++++------------------
 1 files changed, 12 insertions(+), 18 deletions(-)

diff --git a/drivers/dma/fsldma.c b/drivers/dma/fsldma.c index

bb883c0..e3814aa 100644

--- a/drivers/dma/fsldma.c
+++ b/drivers/dma/fsldma.c

@@ -645,10 +645,9 @@ static dma_cookie_t fsl_dma_tx_submit(struct

dma_async_tx_descriptor *tx)

quoted

 	struct fsldma_chan *chan = to_fsl_chan(tx->chan);
 	struct fsl_desc_sw *desc = tx_to_fsl_desc(tx);
 	struct fsl_desc_sw *child;
-	unsigned long flags;
 	dma_cookie_t cookie;

-	spin_lock_irqsave(&chan->desc_lock, flags);
+	spin_lock_bh(&chan->desc_lock);

 	/*
 	 * assign cookies to all of the software descriptors @@ -661,7
+660,7 @@ static dma_cookie_t fsl_dma_tx_submit(struct

dma_async_tx_descriptor *tx)

quoted

 	/* put this transaction onto the tail of the pending queue */
 	append_ld_queue(chan, desc);

-	spin_unlock_irqrestore(&chan->desc_lock, flags);
+	spin_unlock_bh(&chan->desc_lock);

 	return cookie;
 }

@@ -770,15 +769,14 @@ static void fsldma_free_desc_list_reverse(struct

fsldma_chan *chan,  static void fsl_dma_free_chan_resources(struct
dma_chan *dchan)  {
 	struct fsldma_chan *chan = to_fsl_chan(dchan);
-	unsigned long flags;

 	chan_dbg(chan, "free all channel resources\n");
-	spin_lock_irqsave(&chan->desc_lock, flags);
+	spin_lock_bh(&chan->desc_lock);
 	fsldma_cleanup_descriptor(chan);
 	fsldma_free_desc_list(chan, &chan->ld_pending);
 	fsldma_free_desc_list(chan, &chan->ld_running);
 	fsldma_free_desc_list(chan, &chan->ld_completed);
-	spin_unlock_irqrestore(&chan->desc_lock, flags);
+	spin_unlock_bh(&chan->desc_lock);

 	dma_pool_destroy(chan->desc_pool);
 	chan->desc_pool = NULL;

@@ -997,7 +995,6 @@ static int fsl_dma_device_control(struct dma_chan

*dchan,  {
 	struct dma_slave_config *config;
 	struct fsldma_chan *chan;
-	unsigned long flags;
 	int size;

 	if (!dchan)

@@ -1007,7 +1004,7 @@ static int fsl_dma_device_control(struct

dma_chan *dchan,

 	switch (cmd) {
 	case DMA_TERMINATE_ALL:
-		spin_lock_irqsave(&chan->desc_lock, flags);
+		spin_lock_bh(&chan->desc_lock);

 		/* Halt the DMA engine */
 		dma_halt(chan);

@@ -1017,7 +1014,7 @@ static int fsl_dma_device_control(struct dma_chan

*dchan,

quoted

 		fsldma_free_desc_list(chan, &chan->ld_running);
 		chan->idle = true;

-		spin_unlock_irqrestore(&chan->desc_lock, flags);
+		spin_unlock_bh(&chan->desc_lock);
 		return 0;

 	case DMA_SLAVE_CONFIG:

@@ -1059,11 +1056,10 @@ static int fsl_dma_device_control(struct

dma_chan *dchan,  static void fsl_dma_memcpy_issue_pending(struct
dma_chan *dchan)  {
 	struct fsldma_chan *chan = to_fsl_chan(dchan);
-	unsigned long flags;

-	spin_lock_irqsave(&chan->desc_lock, flags);
+	spin_lock_bh(&chan->desc_lock);
 	fsl_chan_xfer_ld_queue(chan);
-	spin_unlock_irqrestore(&chan->desc_lock, flags);
+	spin_unlock_bh(&chan->desc_lock);
 }

 /**

@@ -1076,15 +1072,14 @@ static enum dma_status fsl_tx_status(struct

dma_chan *dchan,  {
 	struct fsldma_chan *chan = to_fsl_chan(dchan);
 	enum dma_status ret;
-	unsigned long flags;

 	ret = dma_cookie_status(dchan, cookie, txstate);
 	if (ret == DMA_SUCCESS)
 		return ret;

-	spin_lock_irqsave(&chan->desc_lock, flags);
+	spin_lock_bh(&chan->desc_lock);
 	fsldma_cleanup_descriptor(chan);
-	spin_unlock_irqrestore(&chan->desc_lock, flags);
+	spin_unlock_bh(&chan->desc_lock);

 	return dma_cookie_status(dchan, cookie, txstate);  } @@ -1163,11
+1158,10 @@ static irqreturn_t fsldma_chan_irq(int irq, void *data)
static void dma_do_tasklet(unsigned long data)  {
 	struct fsldma_chan *chan = (struct fsldma_chan *)data;
-	unsigned long flags;

 	chan_dbg(chan, "tasklet entry\n");

-	spin_lock_irqsave(&chan->desc_lock, flags);
+	spin_lock_bh(&chan->desc_lock);

 	/* the hardware is now idle and ready for more */
 	chan->idle = true;

@@ -1175,7 +1169,7 @@ static void dma_do_tasklet(unsigned long data)
 	/* Run all cleanup for this descriptor */
 	fsldma_cleanup_descriptor(chan);

-	spin_unlock_irqrestore(&chan->desc_lock, flags);
+	spin_unlock_bh(&chan->desc_lock);

 	chan_dbg(chan, "tasklet exit\n");
 }
--

1.7.5.1


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