[PATCH v3 3/6] dma: rcar-dma: check if complete DMA packet received but not processed

[PATCH v3 3/6] dma: rcar-dma: check if complete DMA packet received but not processed

[hamzahfrq.sub]

From: Muhammad Hamza Farooq <mfarooq@visteon.com>

At high speeds, DMA interrupts come very fast. If there's an interrupt
pending before previous is handled, this method can help return actual
status of the DMA transaction by reading the hardware flag

Signed-off-by: Muhammad Hamza Farooq <mfarooq@visteon.com>
---
 drivers/dma/sh/rcar-dmac.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
index c7cd4ed..6c806d0 100644
--- a/drivers/dma/sh/rcar-dmac.c
+++ b/drivers/dma/sh/rcar-dmac.c
@@ -314,6 +314,14 @@ static bool rcar_dmac_chan_is_busy(struct rcar_dmac_chan *chan)
 	return (chcr & (RCAR_DMACHCR_DE | RCAR_DMACHCR_TE)) = RCAR_DMACHCR_DE;
 }
 
+/* Transfer completed but not yet handled */
+static bool rcar_dmac_last_tx_complete(struct rcar_dmac_chan *chan)
+{
+	u32 chcr = rcar_dmac_chan_read(chan, RCAR_DMACHCR);
+
+	return (chcr & RCAR_DMACHCR_TE) = RCAR_DMACHCR_TE;
+}
+
 static void rcar_dmac_chan_start_xfer(struct rcar_dmac_chan *chan)
 {
 	struct rcar_dmac_desc *desc = chan->desc.running;
@@ -1238,6 +1246,10 @@ static enum dma_status rcar_dmac_tx_status(struct dma_chan *chan,
 	unsigned long flags;
 	unsigned int residue;
 
+	/* Interrupt not yet serviced */
+	if (rcar_dmac_last_tx_complete(rchan))
+		return DMA_COMPLETE;
+
 	status = dma_cookie_status(chan, cookie, txstate);
 	if (status = DMA_COMPLETE || !txstate)
 		return status;
-- 
1.9.1

Re: [PATCH v3 3/6] dma: rcar-dma: check if complete DMA packet received but not processed

[Vinod Koul]

On Tue, Sep 29, 2015 at 10:44:45PM +0200, hamzahfrq.sub@gmail.com wrote:
> From: Muhammad Hamza Farooq <mfarooq@visteon.com>
> 
> At high speeds, DMA interrupts come very fast. If there's an interrupt
> pending before previous is handled, this method can help return actual

which method ??

> status of the DMA transaction by reading the hardware flag

-- 
~Vinod

Re: [PATCH v3 3/6] dma: rcar-dma: check if complete DMA packet received but not processed

[Laurent Pinchart]

Hi Muhammad,

Thank you for the patch.

On Tuesday 29 September 2015 22:44:45 hamzahfrq.sub@gmail.com wrote:
> From: Muhammad Hamza Farooq <mfarooq@visteon.com>
> 
> At high speeds, DMA interrupts come very fast. If there's an interrupt
> pending before previous is handled, this method can help return actual
> status of the DMA transaction by reading the hardware flag
> 
> Signed-off-by: Muhammad Hamza Farooq <mfarooq@visteon.com>
> ---
>  drivers/dma/sh/rcar-dmac.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
> index c7cd4ed..6c806d0 100644
> --- a/drivers/dma/sh/rcar-dmac.c
> +++ b/drivers/dma/sh/rcar-dmac.c
> @@ -314,6 +314,14 @@ static bool rcar_dmac_chan_is_busy(struct
> rcar_dmac_chan *chan) return (chcr & (RCAR_DMACHCR_DE | RCAR_DMACHCR_TE))
> = RCAR_DMACHCR_DE; }
> 
> +/* Transfer completed but not yet handled */
> +static bool rcar_dmac_last_tx_complete(struct rcar_dmac_chan *chan)
> +{
> +	u32 chcr = rcar_dmac_chan_read(chan, RCAR_DMACHCR);
> +
> +	return (chcr & RCAR_DMACHCR_TE) = RCAR_DMACHCR_TE;
> +}
> +
>  static void rcar_dmac_chan_start_xfer(struct rcar_dmac_chan *chan)
>  {
>  	struct rcar_dmac_desc *desc = chan->desc.running;
> @@ -1238,6 +1246,10 @@ static enum dma_status rcar_dmac_tx_status(struct
> dma_chan *chan, unsigned long flags;
>  	unsigned int residue;
> 
> +	/* Interrupt not yet serviced */
> +	if (rcar_dmac_last_tx_complete(rchan))
> +		return DMA_COMPLETE;
> +

I don't think this will work. In particular rcar_dmac_tx_status() can be 
called with a cookie corresponding to a transfer not yet scheduled. A pending 
transfer complete interrupt doesn't mean that that cookie is complete.

Furthermore I'm not sure this will really improve performances. The 
dma_cookie_status() call below just compares cookie values, I don't expect it 
to be much slower than a register read.

>  	status = dma_cookie_status(chan, cookie, txstate);
>  	if (status = DMA_COMPLETE || !txstate)
>  		return status;

-- 
Regards,

Laurent Pinchart