[2/2] dmaengine i.MX SDMA: protect channel0
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Message ID 1291630198-9690-3-git-send-email-s.hauer@pengutronix.de
State New, archived
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Series
  • [1/2] dmaengine i.MX SDMA: initialize on module_init
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Commit Message

Sascha Hauer Dec. 6, 2010, 10:09 a.m. UTC
Channel 0 of the SDMA engine is a shared resource used by the
other channels, thus we have to protect it with a mutex.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 drivers/dma/imx-sdma.c |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

Comments

Dan Williams Dec. 7, 2010, 11:50 p.m. UTC | #1
On Mon, Dec 6, 2010 at 2:09 AM, Sascha Hauer <s.hauer@pengutronix.de> wrote:
> Channel 0 of the SDMA engine is a shared resource used by the
> other channels, thus we have to protect it with a mutex.
>
> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> ---

This one is not making sense to me...

>  drivers/dma/imx-sdma.c |   11 +++++++++++
>  1 files changed, 11 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
> index 01c4a5f..b1f5947 100644
> --- a/drivers/dma/imx-sdma.c
> +++ b/drivers/dma/imx-sdma.c
> @@ -355,6 +355,7 @@ struct sdma_engine {
>        struct dma_device               dma_device;
>        struct clk                      *clk;
>        struct sdma_script_start_addrs  *script_addrs;
> +       struct mutex                    channel0_mutex;
>  };
>
>  #define SDMA_H_CONFIG_DSPDMA   (1 << 12) /* indicates if the DSPDMA is used */
> @@ -437,6 +438,8 @@ static int sdma_load_script(struct sdma_engine *sdma, void *buf, int size,
>        if (!buf_virt)
>                return -ENOMEM;
>
> +       mutex_lock(&sdma->channel0_mutex);
> +
>        bd0->mode.command = C0_SETPM;
>        bd0->mode.status = BD_DONE | BD_INTR | BD_WRAP | BD_EXTD;
>        bd0->mode.count = size / 2;
> @@ -447,6 +450,8 @@ static int sdma_load_script(struct sdma_engine *sdma, void *buf, int size,
>
>        ret = sdma_run_channel(&sdma->channel[0]);
>
> +       mutex_unlock(&sdma->channel0_mutex);
> +

In sdma_load_script() what data structure are we protecting at single
threaded init time prior to registering channels?

>        dma_free_coherent(NULL, size, buf_virt, buf_phys);
>
>        return ret;

> @@ -684,6 +689,8 @@ static int sdma_load_context(struct sdma_channel *sdmac)
>        context->gReg[6] = sdmac->shp_addr;
>        context->gReg[7] = sdmac->watermark_level;
>
> +       mutex_lock(&sdma->channel0_mutex);
> +
>        bd0->mode.command = C0_SETDM;
>        bd0->mode.status = BD_DONE | BD_INTR | BD_WRAP | BD_EXTD;
>        bd0->mode.count = sizeof(*context) / 4;
> @@ -692,6 +699,8 @@ static int sdma_load_context(struct sdma_channel *sdmac)
>
>        ret = sdma_run_channel(&sdma->channel[0]);
>
> +       mutex_unlock(&sdma->channel0_mutex);
> +

This sdma_load_context() is called from various ->prep() contexts.
What guarantees are there that we can sleep in these contexts?  At
least ->prep_memcpy() might be called in a atomic context.  I have
been assuming the same for all prep routines across archs.

--
Dan
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Sascha Hauer Dec. 9, 2010, 2:50 p.m. UTC | #2
On Tue, Dec 07, 2010 at 03:50:33PM -0800, Dan Williams wrote:
> On Mon, Dec 6, 2010 at 2:09 AM, Sascha Hauer <s.hauer@pengutronix.de> wrote:
> > Channel 0 of the SDMA engine is a shared resource used by the
> > other channels, thus we have to protect it with a mutex.
> >
> > Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> > ---
> 
> This one is not making sense to me...
> 
> >  drivers/dma/imx-sdma.c |   11 +++++++++++
> >  1 files changed, 11 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
> > index 01c4a5f..b1f5947 100644
> > --- a/drivers/dma/imx-sdma.c
> > +++ b/drivers/dma/imx-sdma.c
> > @@ -355,6 +355,7 @@ struct sdma_engine {
> >        struct dma_device               dma_device;
> >        struct clk                      *clk;
> >        struct sdma_script_start_addrs  *script_addrs;
> > +       struct mutex                    channel0_mutex;
> >  };
> >
> >  #define SDMA_H_CONFIG_DSPDMA   (1 << 12) /* indicates if the DSPDMA is used */
> > @@ -437,6 +438,8 @@ static int sdma_load_script(struct sdma_engine *sdma, void *buf, int size,
> >        if (!buf_virt)
> >                return -ENOMEM;
> >
> > +       mutex_lock(&sdma->channel0_mutex);
> > +
> >        bd0->mode.command = C0_SETPM;
> >        bd0->mode.status = BD_DONE | BD_INTR | BD_WRAP | BD_EXTD;
> >        bd0->mode.count = size / 2;
> > @@ -447,6 +450,8 @@ static int sdma_load_script(struct sdma_engine *sdma, void *buf, int size,
> >
> >        ret = sdma_run_channel(&sdma->channel[0]);
> >
> > +       mutex_unlock(&sdma->channel0_mutex);
> > +
> 
> In sdma_load_script() what data structure are we protecting at single
> threaded init time prior to registering channels?

At the moment the lock in sdma_load_script is not needed, but I have a
patch in the queue using request_firmware_nowait instead of
request_firmware, so the firmware might come in after initialization
(The SDMA does not really depend on the firmware, it can just offer more
features when it is available)

> 
> >        dma_free_coherent(NULL, size, buf_virt, buf_phys);
> >
> >        return ret;
> 
> > @@ -684,6 +689,8 @@ static int sdma_load_context(struct sdma_channel *sdmac)
> >        context->gReg[6] = sdmac->shp_addr;
> >        context->gReg[7] = sdmac->watermark_level;
> >
> > +       mutex_lock(&sdma->channel0_mutex);
> > +
> >        bd0->mode.command = C0_SETDM;
> >        bd0->mode.status = BD_DONE | BD_INTR | BD_WRAP | BD_EXTD;
> >        bd0->mode.count = sizeof(*context) / 4;
> > @@ -692,6 +699,8 @@ static int sdma_load_context(struct sdma_channel *sdmac)
> >
> >        ret = sdma_run_channel(&sdma->channel[0]);
> >
> > +       mutex_unlock(&sdma->channel0_mutex);
> > +
> 
> This sdma_load_context() is called from various ->prep() contexts.
> What guarantees are there that we can sleep in these contexts?  At
> least ->prep_memcpy() might be called in a atomic context.  I have
> been assuming the same for all prep routines across archs.

Currently it is only called from non interrupt context.

Fact is that we need some kind of locking because channel 0 is used by
the other channels. I just made a check and it shows running channel 0
only takes about 6us, so a spinlock might be a better weapon here.

So forget this patch for now and I'll send an updated one using a
spinlock (and no completion interrupt for channel 0).

Sascha

Patch
diff mbox series

diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
index 01c4a5f..b1f5947 100644
--- a/drivers/dma/imx-sdma.c
+++ b/drivers/dma/imx-sdma.c
@@ -355,6 +355,7 @@  struct sdma_engine {
 	struct dma_device		dma_device;
 	struct clk			*clk;
 	struct sdma_script_start_addrs	*script_addrs;
+	struct mutex			channel0_mutex;
 };
 
 #define SDMA_H_CONFIG_DSPDMA	(1 << 12) /* indicates if the DSPDMA is used */
@@ -437,6 +438,8 @@  static int sdma_load_script(struct sdma_engine *sdma, void *buf, int size,
 	if (!buf_virt)
 		return -ENOMEM;
 
+	mutex_lock(&sdma->channel0_mutex);
+
 	bd0->mode.command = C0_SETPM;
 	bd0->mode.status = BD_DONE | BD_INTR | BD_WRAP | BD_EXTD;
 	bd0->mode.count = size / 2;
@@ -447,6 +450,8 @@  static int sdma_load_script(struct sdma_engine *sdma, void *buf, int size,
 
 	ret = sdma_run_channel(&sdma->channel[0]);
 
+	mutex_unlock(&sdma->channel0_mutex);
+
 	dma_free_coherent(NULL, size, buf_virt, buf_phys);
 
 	return ret;
@@ -684,6 +689,8 @@  static int sdma_load_context(struct sdma_channel *sdmac)
 	context->gReg[6] = sdmac->shp_addr;
 	context->gReg[7] = sdmac->watermark_level;
 
+	mutex_lock(&sdma->channel0_mutex);
+
 	bd0->mode.command = C0_SETDM;
 	bd0->mode.status = BD_DONE | BD_INTR | BD_WRAP | BD_EXTD;
 	bd0->mode.count = sizeof(*context) / 4;
@@ -692,6 +699,8 @@  static int sdma_load_context(struct sdma_channel *sdmac)
 
 	ret = sdma_run_channel(&sdma->channel[0]);
 
+	mutex_unlock(&sdma->channel0_mutex);
+
 	return ret;
 }
 
@@ -1297,6 +1306,8 @@  static int __init sdma_probe(struct platform_device *pdev)
 
 	sdma->version = pdata->sdma_version;
 
+	mutex_init(&sdma->channel0_mutex);
+
 	INIT_LIST_HEAD(&sdma->dma_device.channels);
 	/* Initialize channel parameters */
 	for (i = 0; i < MAX_DMA_CHANNELS; i++) {