leandrof/linux
1
0
Fork 0
forked from Minki/linux
Code Issues Pull Requests Packages Projects Releases Wiki Activity

dma: mxs-dma: Use semaphores for cyclic DMA

Browse Source 
mxs dma channel hardware reset command is not reliable and can cause
a channel stall. The only way to fix the channel stall is a DMA engine
reset.

To avoid channel resets we use the hardware semaphore counter. For each
transmitted segment, the DMA channel will decrease the counter by one.
To use this mechanism with cyclic DMA, we need to increase the semaphore
counter with each completed DMA command in the interrupt handler. To
avoid any interruptions between the DMA transfers, the semaphore counter
is initialized with 2. This way the counter can be increased in the
interrupt handler without an influence on the transfer of the DMA
engine.

When disabling the channel, we stop increasing the semaphore counter in
the interrupt handler.

This patch was tested on i.MX28 with the SAIF DMA channel.

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
This commit is contained in:
Markus Pargmann 2013-10-29 08:47:49 +01:00 committed by Vinod Koul
parent bb3660f130
commit 2dcbdce361
1 changed files with 35 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

41
drivers/dma/mxs-dma.c
View File

@ -119,7 +119,9 @@ struct mxs_dma_chan {
int desc_count;
enum dma_status status;
unsigned int flags;
bool reset;
#define MXS_DMA_SG_LOOP (1 << 0)
#define MXS_DMA_USE_SEMAPHORE (1 << 1)
};
#define MXS_DMA_CHANNELS 16
@ -205,7 +207,17 @@ static void mxs_dma_reset_chan(struct mxs_dma_chan *mxs_chan)
struct mxs_dma_engine *mxs_dma = mxs_chan->mxs_dma;
int chan_id = mxs_chan->chan.chan_id;
if (dma_is_apbh(mxs_dma) && apbh_is_old(mxs_dma)) {
/*
* mxs dma channel resets can cause a channel stall. To recover from a
* channel stall, we have to reset the whole DMA engine. To avoid this,
* we use cyclic DMA with semaphores, that are enhanced in
* mxs_dma_int_handler. To reset the channel, we can simply stop writing
* into the semaphore counter.
*/
if (mxs_chan->flags & MXS_DMA_USE_SEMAPHORE &&
mxs_chan->flags & MXS_DMA_SG_LOOP) {
mxs_chan->reset = true;
} else if (dma_is_apbh(mxs_dma) && apbh_is_old(mxs_dma)) {
writel(1 << (chan_id + BP_APBH_CTRL0_RESET_CHANNEL),
mxs_dma->base + HW_APBHX_CTRL0 + STMP_OFFSET_REG_SET);
} else {
@ -231,7 +243,6 @@ static void mxs_dma_reset_chan(struct mxs_dma_chan *mxs_chan)
"Failed waiting for the DMA channel %d to leave state READ_FLUSH, trying to reset channel in READ_FLUSH state now\n",
chan_id);
writel(1 << (chan_id + BP_APBHX_CHANNEL_CTRL_RESET_CHANNEL),
mxs_dma->base + HW_APBHX_CHANNEL_CTRL + STMP_OFFSET_REG_SET);
}
@ -249,7 +260,16 @@ static void mxs_dma_enable_chan(struct mxs_dma_chan *mxs_chan)
mxs_dma->base + HW_APBHX_CHn_NXTCMDAR(mxs_dma, chan_id));
/* write 1 to SEMA to kick off the channel */
writel(1, mxs_dma->base + HW_APBHX_CHn_SEMA(mxs_dma, chan_id));
if (mxs_chan->flags & MXS_DMA_USE_SEMAPHORE &&
mxs_chan->flags & MXS_DMA_SG_LOOP) {
/* A cyclic DMA consists of at least 2 segments, so initialize
* the semaphore with 2 so we have enough time to add 1 to the
* semaphore if we need to */
writel(2, mxs_dma->base + HW_APBHX_CHn_SEMA(mxs_dma, chan_id));
} else {
writel(1, mxs_dma->base + HW_APBHX_CHn_SEMA(mxs_dma, chan_id));
}
mxs_chan->reset = false;
}
static void mxs_dma_disable_chan(struct mxs_dma_chan *mxs_chan)
@ -365,14 +385,21 @@ static irqreturn_t mxs_dma_int_handler(int irq, void *dev_id)
mxs_chan->status = DMA_ERROR;
mxs_dma_reset_chan(mxs_chan);
} else if (mxs_chan->status != DMA_COMPLETE) {
if (mxs_chan->flags & MXS_DMA_SG_LOOP)
if (mxs_chan->flags & MXS_DMA_SG_LOOP) {
mxs_chan->status = DMA_IN_PROGRESS;
else
if (mxs_chan->flags & MXS_DMA_USE_SEMAPHORE)
writel(1, mxs_dma->base +
HW_APBHX_CHn_SEMA(mxs_dma, chan));
} else {
mxs_chan->status = DMA_COMPLETE;
}
}
if (mxs_chan->status == DMA_COMPLETE)
if (mxs_chan->status == DMA_COMPLETE) {
if (mxs_chan->reset)
return IRQ_HANDLED;
dma_cookie_complete(&mxs_chan->desc);
}
/* schedule tasklet on this channel */
tasklet_schedule(&mxs_chan->tasklet);
@ -576,6 +603,7 @@ static struct dma_async_tx_descriptor *mxs_dma_prep_dma_cyclic(
mxs_chan->status = DMA_IN_PROGRESS;
mxs_chan->flags |= MXS_DMA_SG_LOOP;
mxs_chan->flags |= MXS_DMA_USE_SEMAPHORE;
if (num_periods > NUM_CCW) {
dev_err(mxs_dma->dma_device.dev,
@ -607,6 +635,7 @@ static struct dma_async_tx_descriptor *mxs_dma_prep_dma_cyclic(
ccw->bits |= CCW_IRQ;
ccw->bits |= CCW_HALT_ON_TERM;
ccw->bits |= CCW_TERM_FLUSH;
ccw->bits |= CCW_DEC_SEM;
ccw->bits |= BF_CCW(direction == DMA_DEV_TO_MEM ?
MXS_DMA_CMD_WRITE : MXS_DMA_CMD_READ, COMMAND);