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SubjectRe: [RFC v2 PATCH 7/7] dmaengine: xilinx_dma: Program interrupt delay timeout
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On 4/9/21 7:56 PM, Radhey Shyam Pandey wrote:
> Program IRQDelay for AXI DMA. The interrupt timeout mechanism causes
> the DMA engine to generate an interrupt after the delay time period
> has expired. It enables dmaengine to respond in real-time even though
> interrupt coalescing is configured. It also remove the placeholder
> for delay interrupt and merge it with frame completion interrupt.
> Since by default interrupt delay timeout is disabled this feature
> addition has no functional impact on VDMA and CDMA IP's.

In my opinion this should not come from the devicetree. This setting is
application specific and should be configured through a runtime API.

For the VDMA there is already xilinx_vdma_channel_set_config() which
allows to configure the maximum number of IRQs that can be coalesced and
the IRQ delay. Something similar is probably needed for the AXIDMA.

>
> Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
> ---
> Changes for v2:
> - Read irq delay timeout value from DT.
> - Merge interrupt processing for frame done and delay interrupt.
> ---
> drivers/dma/xilinx/xilinx_dma.c | 20 +++++++++++---------
> 1 file changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
> index a2ea2d649332..0c0dc9882a01 100644
> --- a/drivers/dma/xilinx/xilinx_dma.c
> +++ b/drivers/dma/xilinx/xilinx_dma.c
> @@ -173,8 +173,10 @@
> #define XILINX_DMA_MAX_TRANS_LEN_MAX 23
> #define XILINX_DMA_V2_MAX_TRANS_LEN_MAX 26
> #define XILINX_DMA_CR_COALESCE_MAX GENMASK(23, 16)
> +#define XILINX_DMA_CR_DELAY_MAX GENMASK(31, 24)
> #define XILINX_DMA_CR_CYCLIC_BD_EN_MASK BIT(4)
> #define XILINX_DMA_CR_COALESCE_SHIFT 16
> +#define XILINX_DMA_CR_DELAY_SHIFT 24
> #define XILINX_DMA_BD_SOP BIT(27)
> #define XILINX_DMA_BD_EOP BIT(26)
> #define XILINX_DMA_BD_COMP_MASK BIT(31)
> @@ -410,6 +412,7 @@ struct xilinx_dma_tx_descriptor {
> * @stop_transfer: Differentiate b/w DMA IP's quiesce
> * @tdest: TDEST value for mcdma
> * @has_vflip: S2MM vertical flip
> + * @irq_delay: Interrupt delay timeout
> */
> struct xilinx_dma_chan {
> struct xilinx_dma_device *xdev;
> @@ -447,6 +450,7 @@ struct xilinx_dma_chan {
> int (*stop_transfer)(struct xilinx_dma_chan *chan);
> u16 tdest;
> bool has_vflip;
> + u8 irq_delay;
> };
>
> /**
> @@ -1555,6 +1559,9 @@ static void xilinx_dma_start_transfer(struct xilinx_dma_chan *chan)
> if (chan->has_sg)
> xilinx_write(chan, XILINX_DMA_REG_CURDESC,
> head_desc->async_tx.phys);
> + reg &= ~XILINX_DMA_CR_DELAY_MAX;
> + reg |= chan->irq_delay << XILINX_DMA_CR_DELAY_SHIFT;
> + dma_ctrl_write(chan, XILINX_DMA_REG_DMACR, reg);
>
> xilinx_dma_start(chan);
>
> @@ -1877,15 +1884,8 @@ static irqreturn_t xilinx_dma_irq_handler(int irq, void *data)
> }
> }
>
> - if (status & XILINX_DMA_DMASR_DLY_CNT_IRQ) {
> - /*
> - * Device takes too long to do the transfer when user requires
> - * responsiveness.
> - */
> - dev_dbg(chan->dev, "Inter-packet latency too long\n");
> - }
> -
> - if (status & XILINX_DMA_DMASR_FRM_CNT_IRQ) {
> + if (status & (XILINX_DMA_DMASR_FRM_CNT_IRQ |
> + XILINX_DMA_DMASR_DLY_CNT_IRQ)) {
> spin_lock(&chan->lock);
> xilinx_dma_complete_descriptor(chan);
> chan->idle = true;
> @@ -2802,6 +2802,8 @@ static int xilinx_dma_chan_probe(struct xilinx_dma_device *xdev,
> /* Retrieve the channel properties from the device tree */
> has_dre = of_property_read_bool(node, "xlnx,include-dre");
>
> + of_property_read_u8(node, "xlnx,irq-delay", &chan->irq_delay);
> +
> chan->genlock = of_property_read_bool(node, "xlnx,genlock-mode");
>
> err = of_property_read_u32(node, "xlnx,datawidth", &value);


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