Alan Stern wrote:
> On Mon, 12 Aug 2013, Takashi Iwai wrote:
>> So... Clemens, Daniel, Eldad, could you guys review the latest version
>> of Alan's patch? I'd love to sort this out for 3.12.
>
> Here's a revised version of the patch (still untested).
> - maxsize = ((ep->freqmax + 0xffff) * (frame_bits >> 3))
> - >> (16 - ep->datainterval);
> + maxsize = ((ep->freqmax + 0xffff) >> (16 - ep->datainterval))
> + * (frame_bits >> 3);
What do you assume prevents firmware writers from splitting frames
across packages? The specification? Sanity? :) (see txfr_quirk)
> The difference is that this version tries always to keep a period's
> worth of bytes in the USB hardware queue.
Having truncated URBs is possible only when URBs are shorter than one
period, so I think that a queue length of at least two periods, together
with a minimum period size, should ensure the isochrounous scheduling
threshold.
This isn't tested either.
Regards,
Clemens
sound/usb/endpoint.c | 3 ++-
sound/usb/pcm.c | 16 ++++++++++++++--
2 files changed, 16 insertions(+), 3 deletions(-)
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -638,7 +638,8 @@ static int data_ep_set_params(struct snd_usb_endpoint *ep,
if (sync_ep)
minsize -= minsize >> 3;
minsize = max(minsize, 1u);
- total_packs = (period_bytes + minsize - 1) / minsize;
+ /* try to make the queue length the same as two periods */
+ total_packs = (2 * period_bytes + minsize - 1) / minsize;
/* we need at least two URBs for queueing */
if (total_packs < 2) {
total_packs = 2;
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -1131,10 +1131,22 @@ static int setup_hw_info(struct snd_pcm_runtime *runtime, struct snd_usb_substre
return err;
param_period_time_if_needed = SNDRV_PCM_HW_PARAM_PERIOD_TIME;
- if (subs->speed == USB_SPEED_FULL)
+ switch (subs->speed) {
+ case USB_SPEED_FULL:
/* full speed devices have fixed data packet interval */
ptmin = 1000;
- if (ptmin == 1000)
+ break;
+ case USB_SPEED_HIGH:
+ /*
+ * Assume we have an EHCI controller with an Isochronous
+ * Scheduling Threshold of one frame (8 microframes), and
+ * add 2 microframes for boundary cases. Increase by 4%
+ * to have a margin for clock inaccuracies.
+ */
+ ptmin = max(ptmin, (8 + 2) * 130u);
+ break;
+ }
+ if (ptmin >= 1000)
/* if period time doesn't go below 1 ms, no rules needed */
param_period_time_if_needed = -1;
snd_pcm_hw_constraint_minmax(runtime, SNDRV_PCM_HW_PARAM_PERIOD_TIME,
--
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