The BCM2835 DMA driver currently requests an interrupt from the
controller regardless whether or not the client has passed in the
DMA_PREP_INTERRUPT flag. This causes unnecessary overhead for cyclic
transactions which do not need an interrupt after each period.
We're about to add such a use case, namely cyclic clearing of the SPI
controller's RX FIFO, so amend the DMA driver to request an interrupt
only if DMA_PREP_INTERRUPT was passed in. Ignore the period_len for
such transactions and set it to the buffer length to make the driver's
calculations work.
Tested-by: Nuno Sá <nuno.sa@xxxxxxxxxx>
Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
Cc: Martin Sperl <kernel@xxxxxxxxxxxxxxxx>
Cc: Florian Kauer <florian.kauer@xxxxxxxx>
---
drivers/dma/bcm2835-dma.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/drivers/dma/bcm2835-dma.c b/drivers/dma/bcm2835-dma.c
index 523c507ad69e..a65514fcb7f2 100644
--- a/drivers/dma/bcm2835-dma.c
+++ b/drivers/dma/bcm2835-dma.c
@@ -691,7 +691,7 @@ static struct dma_async_tx_descriptor *bcm2835_dma_prep_dma_cyclic(
struct bcm2835_desc *d;
dma_addr_t src, dst;
u32 info = BCM2835_DMA_WAIT_RESP;
- u32 extra = BCM2835_DMA_INT_EN;
+ u32 extra = 0;
size_t max_len = bcm2835_dma_max_frame_length(c);
size_t frames;
@@ -707,6 +707,11 @@ static struct dma_async_tx_descriptor *bcm2835_dma_prep_dma_cyclic(
return NULL;
}
+ if (flags & DMA_PREP_INTERRUPT)
+ extra |= BCM2835_DMA_INT_EN;
+ else
+ period_len = buf_len;
+
/*
* warn if buf_len is not a multiple of period_len - this may leed
* to unexpected latencies for interrupts and thus audiable clicks
@@ -778,7 +783,10 @@ static int bcm2835_dma_terminate_all(struct dma_chan *chan)
/* stop DMA activity */
if (c->desc) {
- vchan_terminate_vdesc(&c->desc->vd);
+ if (c->desc->vd.tx.flags & DMA_PREP_INTERRUPT)
+ vchan_terminate_vdesc(&c->desc->vd);
+ else
+ vchan_vdesc_fini(&c->desc->vd);
c->desc = NULL;
bcm2835_dma_abort(c);
}
--
2.20.1
