[PATCH v2] dmaengine: tegra-apb: Support non-flow controlled slave configuration

[Dmitry Osipenko <digetx@xxxxxxxxx>]

This allows DMA client to issue a non-flow controlled TX. In particular
it is needed for the fuse driver that reads fuse registers using APBDMA
to workaround a HW bug that results in hang when CPU and DMA perform
simultaneous access to fuse peripheral.

Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
Reviewed-by: Jon Hunter <jonathanh@xxxxxxxxxx>
---

Change log:

v2:
	- Removed trailing whitespace reported by checkpatch

 drivers/dma/tegra20-apb-dma.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c
index b9d75a54c896..9a558e30c461 100644
--- a/drivers/dma/tegra20-apb-dma.c
+++ b/drivers/dma/tegra20-apb-dma.c
@@ -353,7 +353,8 @@ static int tegra_dma_slave_config(struct dma_chan *dc,
 	}
 
 	memcpy(&tdc->dma_sconfig, sconfig, sizeof(*sconfig));
-	if (tdc->slave_id == TEGRA_APBDMA_SLAVE_ID_INVALID) {
+	if (tdc->slave_id == TEGRA_APBDMA_SLAVE_ID_INVALID &&
+	    sconfig->device_fc) {
 		if (sconfig->slave_id > TEGRA_APBDMA_CSR_REQ_SEL_MASK)
 			return -EINVAL;
 		tdc->slave_id = sconfig->slave_id;
@@ -970,8 +971,13 @@ static struct dma_async_tx_descriptor *tegra_dma_prep_slave_sg(
 					TEGRA_APBDMA_AHBSEQ_WRAP_SHIFT;
 	ahb_seq |= TEGRA_APBDMA_AHBSEQ_BUS_WIDTH_32;
 
-	csr |= TEGRA_APBDMA_CSR_ONCE | TEGRA_APBDMA_CSR_FLOW;
-	csr |= tdc->slave_id << TEGRA_APBDMA_CSR_REQ_SEL_SHIFT;
+	csr |= TEGRA_APBDMA_CSR_ONCE;
+
+	if (tdc->slave_id != TEGRA_APBDMA_SLAVE_ID_INVALID) {
+		csr |= TEGRA_APBDMA_CSR_FLOW;
+		csr |= tdc->slave_id << TEGRA_APBDMA_CSR_REQ_SEL_SHIFT;
+	}
+
 	if (flags & DMA_PREP_INTERRUPT)
 		csr |= TEGRA_APBDMA_CSR_IE_EOC;
 
@@ -1110,10 +1116,13 @@ static struct dma_async_tx_descriptor *tegra_dma_prep_dma_cyclic(
 					TEGRA_APBDMA_AHBSEQ_WRAP_SHIFT;
 	ahb_seq |= TEGRA_APBDMA_AHBSEQ_BUS_WIDTH_32;
 
-	csr |= TEGRA_APBDMA_CSR_FLOW;
+	if (tdc->slave_id != TEGRA_APBDMA_SLAVE_ID_INVALID) {
+		csr |= TEGRA_APBDMA_CSR_FLOW;
+		csr |= tdc->slave_id << TEGRA_APBDMA_CSR_REQ_SEL_SHIFT;
+	}
+
 	if (flags & DMA_PREP_INTERRUPT)
 		csr |= TEGRA_APBDMA_CSR_IE_EOC;
-	csr |= tdc->slave_id << TEGRA_APBDMA_CSR_REQ_SEL_SHIFT;
 
 	apb_seq |= TEGRA_APBDMA_APBSEQ_WRAP_WORD_1;
 
-- 
2.14.2

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