Hi Muhammad,
Thank you for the patch.
On Tuesday 29 September 2015 22:44:45 hamzahfrq.sub@xxxxxxxxx wrote:
> From: Muhammad Hamza Farooq <mfarooq@xxxxxxxxxxx>
>
> 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@xxxxxxxxxxx>
> ---
> 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
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