On 03/02/2017 03:52 AM, Bin Liu wrote:
> The CPPI41 driver polls register to workaround the pre-mature TX
> interrupt issue, but it causes audio playback underrun when triggered in
> Isoch transfers.
>
> Isoch doesn't do back-to-back transfers, the TX should be done by the
> time the next transfer is scheduled. So skip this polling workaround for
> Isoch transfer.
>
> Fixes: a655f481d83d6 ("usb: musb: musb_cppi41: handle pre-mature TX complete interrupt")
> Cc: <stable@xxxxxxxxxxxxxxx> #4.1+
> Reported-by: Alexandre Bailon <abailon@xxxxxxxxxxxx>
> Signed-off-by: Bin Liu <b-liu@xxxxxx>
> ---
> drivers/usb/musb/musb_cppi41.c | 23 +++++++++++++++++++++--
> 1 file changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/musb/musb_cppi41.c b/drivers/usb/musb/musb_cppi41.c
> index 00e272bfee39..355655f8a3fb 100644
> --- a/drivers/usb/musb/musb_cppi41.c
> +++ b/drivers/usb/musb/musb_cppi41.c
> @@ -238,8 +238,27 @@ static void cppi41_dma_callback(void *private_data,
> transferred < cppi41_channel->packet_sz)
> cppi41_channel->prog_len = 0;
>
> - if (cppi41_channel->is_tx)
> - empty = musb_is_tx_fifo_empty(hw_ep);
> + if (cppi41_channel->is_tx) {
> + u8 type;
> +
> + if (is_host_active(musb))
> + type = hw_ep->out_qh->type;
> + else
> + type = hw_ep->ep_in.type;
> +
> + if (type == USB_ENDPOINT_XFER_ISOC)
> + /*
> + * Don't use the early-TX-interrupt workaround below
> + * for Isoch transfter. Since Isoch are periodic
> + * transfer, by the time the next transfer is
> + * scheduled, the current one should be done already.
> + *
> + * This avoids audio playback underrun issue.
> + */
> + empty = true;
> + else
> + empty = musb_is_tx_fifo_empty(hw_ep);
> + }
>
> if (!cppi41_channel->is_tx || empty) {
> cppi41_trans_done(cppi41_channel);
>
Tested on omapl138-lcdk and it significantly decreases the cpu load
and then fixes the underruns.
Tested-by: Alexandre Bailon <abailon@xxxxxxxxxxxx>
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