On Thu, Jan 28, 2016 at 12:29 PM, John Ogness <john.ogness@xxxxxxxxxxxxx> wrote:
> When retrieving the residue value, the SRC/DST fields of the
> active PaRAM are read to determine the current position of
> the DMA engine. However, the AM335x Technical Reference Manual
> states:
> + /*
> + * "pos" may represent a transfer request that is still being
> + * processed by the EDMACC or EDMATC. We will busy wait until
> + * any one of the situations occurs:
> + * 1. the DMA hardware is idle
> + * 2. a new transfer request is setup
> + * 3. we hit the loop limit
> + */
> + while (edma_read(echan->ecc, EDMA_CCSTAT) & EDMA_CCSTAT_ACTV) {
> + /* check if a new transfer request is setup */
> + if (edma_get_position(echan->ecc,
> + echan->slot[0], dst) != pos) {
> + break;
> + }
> +
> + if (!--loop_count) {
More usual pattern is
while (... && --count) {
}
if (!count) {
Timeout!
}
But since it's minor and already applied, just take into consideration
for the future.
> + dev_dbg_ratelimited(echan->vchan.chan.device->dev,
> + "%s: timeout waiting for PaRAM update\n",
> + __func__);
> + break;
> + }
> +
> + cpu_relax();
> + }
--
With Best Regards,
Andy Shevchenko
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