Hello Muhammad,
Thank you for the patch.
On Tuesday 29 September 2015 22:44:43 hamzahfrq.sub@xxxxxxxxx wrote:
> From: Muhammad Hamza Farooq <mfarooq@xxxxxxxxxxx>
>
> DMA engine does not stop instantaneously when transaction is going on
> (see datasheet). Wait has been added
>
> Signed-off-by: Muhammad Hamza Farooq <mfarooq@xxxxxxxxxxx>
> ---
> drivers/dma/sh/rcar-dmac.c | 28 ++++++++++++++++++++++++++--
> 1 file changed, 26 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
> index 7820d07..2b28291 100644
> --- a/drivers/dma/sh/rcar-dmac.c
> +++ b/drivers/dma/sh/rcar-dmac.c
> @@ -716,14 +716,38 @@ static int rcar_dmac_fill_hwdesc(struct rcar_dmac_chan
> *chan, /*
> ---------------------------------------------------------------------------
> * Stop and reset
> */
> +#define NR_READS_TO_WAIT 5 /* number of times to check if DE = 0 */
> +static inline int rcar_dmac_wait_stop(struct rcar_dmac_chan *chan)
> +{
> + unsigned int i = 0;
> +
> + do {
> + u32 chcr = rcar_dmac_chan_read(chan, RCAR_DMACHCR);
> +
> + if (!(chcr & RCAR_DMACHCR_DE))
> + return 0;
> + cpu_relax();
> + dev_dbg(chan->chan.device->dev, "DMA xfer couldn't be stopped");
Would it make sense to move the message out of the loop and use dev_err() ? It
seems like a pretty serious error.
> + } while (++i < NR_READS_TO_WAIT);
How long does the DMA engine typically need to stop ? Is there a safe upper
bound ?
> -static void rcar_dmac_chan_halt(struct rcar_dmac_chan *chan)
> + return -EBUSY;
> +}
> +
> +/* Called with chan lock held */
> +static int rcar_dmac_chan_halt(struct rcar_dmac_chan *chan)
> {
> - u32 chcr = rcar_dmac_chan_read(chan, RCAR_DMACHCR);
> + u32 chcr;
> + int ret;
>
> + chcr = rcar_dmac_chan_read(chan, RCAR_DMACHCR);
> chcr &= ~(RCAR_DMACHCR_DSE | RCAR_DMACHCR_DSIE | RCAR_DMACHCR_IE |
> RCAR_DMACHCR_TE | RCAR_DMACHCR_DE);
> rcar_dmac_chan_write(chan, RCAR_DMACHCR, chcr);
> + ret = rcar_dmac_wait_stop(chan);
As the rcar_dmac_wait_stop() function is used here only I'd inline the code
directly.
> +
> + WARN_ON(ret < 0);
If you use dev_err() instead of dev_dbg() above you could remove the WARN_on.
> +
> + return ret;
> }
>
> static void rcar_dmac_chan_reinit(struct rcar_dmac_chan *chan)
--
Regards,
Laurent Pinchart
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