On 18.02.2016, at 04:24, Eric Anholt [off-list ref] wrote:

kernel at martin.sperl.org writes:

quoted

From: Martin Sperl <redacted>

In preparation of adding slave_sg functionality this patch moves the
generation/allocation of bcm2835_desc and the building of
the corresponding DMA-control-block chain from bcm2835_dma_prep_dma_cyclic
into the newly created method bcm2835_dma_create_cb_chain.

This new code also takes the limits of LITE channels into account
and splits the control-block transfers at the correct location.

Tested Audio output with a Hifiberry I2S card.

Signed-off-by: Martin Sperl <redacted>
---
drivers/dma/bcm2835-dma.c |  288 ++++++++++++++++++++++++++++++---------------
1 file changed, 191 insertions(+), 97 deletions(-)

diff --git a/drivers/dma/bcm2835-dma.c b/drivers/dma/bcm2835-dma.c
index 43758ba..41a4f0b 100644
--- a/drivers/dma/bcm2835-dma.c
+++ b/drivers/dma/bcm2835-dma.c

@@ -90,12 +90,12 @@ struct bcm2835_desc {

	struct virt_dma_desc vd;
	enum dma_transfer_direction dir;

-	struct bcm2835_cb_entry *cb_list;
-
	unsigned int frames;
	size_t size;

	bool cyclic;
+
+	struct bcm2835_cb_entry cb_list[];
};

#define BCM2835_DMA_CS		0x00

@@ -181,6 +181,22 @@ struct bcm2835_desc {

#define BCM2835_DMA_IRQ_SHARED		11
#define BCM2835_DMA_IRQ_ALL		12

+/* the max dma length for different channels */
+#define MAX_DMA_LEN SZ_1G
+#define MAX_LITE_DMA_LEN (SZ_64K - 4)
+
+static inline bool bcm2835_dma_is_lite(struct bcm2835_chan *c)
+{
+	/* dma channels >= 7 are LITE channels */
+	return (c->ch >= 7);
+}

You can ask a channel if it's a LITE engine by checking if the DEBUG reg
has bit 28 set.  Then you don't need to have the software/DT guessing
about it.

I will implement that - it is simple.

However, I'm disappointed to see these changes for adding LITE support
included in the same commit as refactoring chain generation into a
separate function.

I will separate this ?LITE-channel handling? out into a separate patch.

Martin