On Wed, 22 Jun 2011, Kirill Smelkov wrote: > There are cases, when 80% max isochronous bandwidth is too limiting. > > For example I have two USB video capture cards which stream uncompressed > video, and to stream full NTSC + PAL videos we'd need > > NTSC 640x480 YUV422 @30fps ~17.6 MB/s > PAL 720x576 YUV422 @25fps ~19.7 MB/s > > isoc bandwidth. > > Now, due to limited alt settings in capture devices NTSC one ends up > streaming with max_pkt_size=2688 and PAL with max_pkt_size=2892, both > with interval=1. In terms of microframe time allocation this gives > > NTSC ~53us > PAL ~57us > > and together > > ~110us > 100us == 80% of 125us uframe time. > > So those two devices can't work together simultaneously because the'd > over allocate isochronous bandwidth. > > 80% seemed a bit arbitrary to me, and I've tried to raise it to 90% and > both devices started to work together, so I though sometimes it would be > a good idea for users to override hardcoded default of max 80% isoc > bandwidth. > > After all, isn't it a user who should decide how to load the bus? If I > can live with 10% or even 5% bulk bandwidth that should be ok. I'm a USB > newcomer, but that 80% seems to be chosen pretty arbitrary to me, just > to serve as a reasonable default. This seems like the sort of feature somebody might reasonably want to use -- if they know exactly what they're doing. > NOTE: for two streams with max_pkt_size=3072 (worst case) both time > allocation would be 60us+60us=120us which is 96% periodic bandwidth > leaving 4% for bulk and control. I think this should work too. At 480 Mb/s, each microframe holds 7500 bytes (less if you count bit-stuffing). 4% of that is 300 bytes, which is not enough for a 512-byte bulk packet. I think you'd run into trouble trying to do any serious bulk transfers on such a tight schedule. > Signed-off-by: Kirill Smelkov <kirr@xxxxxxxxxx> > Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> > --- > drivers/usb/host/ehci-hcd.c | 16 ++++++++++++++++ > drivers/usb/host/ehci-sched.c | 17 +++++++---------- > 2 files changed, 23 insertions(+), 10 deletions(-) > > diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c > index c606b02..1d36e72 100644 > --- a/drivers/usb/host/ehci-hcd.c > +++ b/drivers/usb/host/ehci-hcd.c > @@ -112,6 +112,14 @@ static unsigned int hird; > module_param(hird, int, S_IRUGO); > MODULE_PARM_DESC(hird, "host initiated resume duration, +1 for each 75us\n"); > > +/* > + * max periodic time per microframe > + * (be careful, USB 2.0 requires it to be 100us = 80% of 125us) > + */ > +static unsigned int uframe_periodic_max = 100; > +module_param(uframe_periodic_max, uint, S_IRUGO); > +MODULE_PARM_DESC(uframe_periodic_max, "maximum allowed periodic part of a microframe, us"); > + This probably should be a sysfs attribute rather than a module parameter, so that it can be applied to individual buses separately. > #define INTR_MASK (STS_IAA | STS_FATAL | STS_PCD | STS_ERR | STS_INT) > > /*-------------------------------------------------------------------------*/ > @@ -571,6 +579,14 @@ static int ehci_init(struct usb_hcd *hcd) > hcc_params = ehci_readl(ehci, &ehci->caps->hcc_params); > > /* > + * tell user, if using non-standard (80% == 100 usec/uframe) bandwidth > + */ > + if (uframe_periodic_max != 100) > + ehci_info(ehci, "using non-standard max periodic bandwith " > + "(%u%% == %u usec/uframe)", > + 100*uframe_periodic_max/125, uframe_periodic_max); > + > + /* Check for invalid values. This should never be less than 100 or greater than 125. > * hw default: 1K periodic list heads, one per frame. > * periodic_size can shrink by USBCMD update if hcc_params allows. > */ > diff --git a/drivers/usb/host/ehci-sched.c b/drivers/usb/host/ehci-sched.c > index d12426f..fb374f2 100644 > --- a/drivers/usb/host/ehci-sched.c > +++ b/drivers/usb/host/ehci-sched.c > @@ -172,7 +172,7 @@ periodic_usecs (struct ehci_hcd *ehci, unsigned frame, unsigned uframe) > } > } > #ifdef DEBUG > - if (usecs > 100) > + if (usecs > uframe_periodic_max) These changes all seem right. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
