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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% set in stone by USB 2.0 specification seems to be
chosen pretty arbitrary to me, just to serve as a reasonable default.
NOTE 1
~~~~~~
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. Alan Stern suggested that bulk then
would be problematic (less than 300*8 bittimes left per microframe), but
I think that is still enough for control traffic.
NOTE 2
~~~~~~
Sarah Sharp expressed concern that maxing out periodic bandwidth
could lead to vendor-specific hardware bugs on host controllers, because
> It's entirely possible that you'll run into
> vendor-specific bugs if you try to pack the schedule with isochronous
> transfers. I don't think any hardware designer would seriously test or
> validate their hardware with a schedule that is basically a violation of
> the USB bus spec (more than 80% for periodic transfers).
So far I've only tested this patch on my HP Mini 5103 with N10 chipset
kirr@mini:~$ lspci
00:00.0 Host bridge: Intel Corporation N10 Family DMI Bridge
00:02.0 VGA compatible controller: Intel Corporation N10 Family Integrated Graphics Controller
00:02.1 Display controller: Intel Corporation N10 Family Integrated Graphics Controller
00:1b.0 Audio device: Intel Corporation N10/ICH 7 Family High Definition Audio Controller (rev 02)
00:1c.0 PCI bridge: Intel Corporation N10/ICH 7 Family PCI Express Port 1 (rev 02)
00:1c.3 PCI bridge: Intel Corporation N10/ICH 7 Family PCI Express Port 4 (rev 02)
00:1d.0 USB Controller: Intel Corporation N10/ICH 7 Family USB UHCI Controller #1 (rev 02)
00:1d.1 USB Controller: Intel Corporation N10/ICH 7 Family USB UHCI Controller #2 (rev 02)
00:1d.2 USB Controller: Intel Corporation N10/ICH 7 Family USB UHCI Controller #3 (rev 02)
00:1d.3 USB Controller: Intel Corporation N10/ICH 7 Family USB UHCI Controller #4 (rev 02)
00:1d.7 USB Controller: Intel Corporation N10/ICH 7 Family USB2 EHCI Controller (rev 02)
00:1e.0 PCI bridge: Intel Corporation 82801 Mobile PCI Bridge (rev e2)
00:1f.0 ISA bridge: Intel Corporation NM10 Family LPC Controller (rev 02)
00:1f.2 SATA controller: Intel Corporation N10/ICH7 Family SATA AHCI Controller (rev 02)
01:00.0 Network controller: Broadcom Corporation BCM4313 802.11b/g/n Wireless LAN Controller (rev 01)
02:00.0 Ethernet controller: Marvell Technology Group Ltd. 88E8059 PCI-E Gigabit Ethernet Controller (rev 11)
and the system works stable with 110us/uframe (~88%) isoc bandwith allocated for
above-mentioned isochronous transfers.
NOTE 3
~~~~~~
This feature is off by default. I mean max periodic bandwidth is set to
100us/uframe by default exactly as it was before the patch. So only those of us
who need the extreme settings are taking the risk - normal users who do not
alter uframe_periodic_max sysfs attribute should not see any change at all.
NOTE 4
~~~~~~
I've tried to update documentation in Documentation/ABI/ thoroughly, but
only "TBD" was put into Documentation/usb/ehci.txt -- the text there seems
to be outdated and much needing refreshing, before it could be amended.
Cc: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Kirill Smelkov <kirr@mns.spb.ru>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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| .. | ||
| whci | ||
| ehci-ath79.c | ||
| ehci-atmel.c | ||
| ehci-au1xxx.c | ||
| ehci-cns3xxx.c | ||
| ehci-dbg.c | ||
| ehci-fsl.c | ||
| ehci-fsl.h | ||
| ehci-grlib.c | ||
| ehci-hcd.c | ||
| ehci-hub.c | ||
| ehci-ixp4xx.c | ||
| ehci-lpm.c | ||
| ehci-mem.c | ||
| ehci-msm.c | ||
| ehci-mxc.c | ||
| ehci-octeon.c | ||
| ehci-omap.c | ||
| ehci-orion.c | ||
| ehci-pci.c | ||
| ehci-pmcmsp.c | ||
| ehci-ppc-of.c | ||
| ehci-ps3.c | ||
| ehci-q.c | ||
| ehci-s5p.c | ||
| ehci-sched.c | ||
| ehci-sh.c | ||
| ehci-spear.c | ||
| ehci-sysfs.c | ||
| ehci-tegra.c | ||
| ehci-vt8500.c | ||
| ehci-w90x900.c | ||
| ehci-xilinx-of.c | ||
| ehci.h | ||
| fhci-dbg.c | ||
| fhci-hcd.c | ||
| fhci-hub.c | ||
| fhci-mem.c | ||
| fhci-q.c | ||
| fhci-sched.c | ||
| fhci-tds.c | ||
| fhci.h | ||
| fsl-mph-dr-of.c | ||
| hwa-hc.c | ||
| imx21-dbg.c | ||
| imx21-hcd.c | ||
| imx21-hcd.h | ||
| isp116x-hcd.c | ||
| isp116x.h | ||
| isp1362-hcd.c | ||
| isp1362.h | ||
| isp1760-hcd.c | ||
| isp1760-hcd.h | ||
| isp1760-if.c | ||
| Kconfig | ||
| Makefile | ||
| octeon2-common.c | ||
| ohci-at91.c | ||
| ohci-ath79.c | ||
| ohci-au1xxx.c | ||
| ohci-cns3xxx.c | ||
| ohci-da8xx.c | ||
| ohci-dbg.c | ||
| ohci-ep93xx.c | ||
| ohci-hcd.c | ||
| ohci-hub.c | ||
| ohci-jz4740.c | ||
| ohci-mem.c | ||
| ohci-octeon.c | ||
| ohci-omap3.c | ||
| ohci-omap.c | ||
| ohci-pci.c | ||
| ohci-pnx4008.c | ||
| ohci-pnx8550.c | ||
| ohci-ppc-of.c | ||
| ohci-ppc-soc.c | ||
| ohci-ps3.c | ||
| ohci-pxa27x.c | ||
| ohci-q.c | ||
| ohci-s3c2410.c | ||
| ohci-sa1111.c | ||
| ohci-sh.c | ||
| ohci-sm501.c | ||
| ohci-spear.c | ||
| ohci-ssb.c | ||
| ohci-tmio.c | ||
| ohci.h | ||
| oxu210hp-hcd.c | ||
| oxu210hp.h | ||
| pci-quirks.c | ||
| pci-quirks.h | ||
| r8a66597-hcd.c | ||
| r8a66597.h | ||
| sl811_cs.c | ||
| sl811-hcd.c | ||
| sl811.h | ||
| u132-hcd.c | ||
| uhci-debug.c | ||
| uhci-grlib.c | ||
| uhci-hcd.c | ||
| uhci-hcd.h | ||
| uhci-hub.c | ||
| uhci-pci.c | ||
| uhci-q.c | ||
| xhci-dbg.c | ||
| xhci-ext-caps.h | ||
| xhci-hub.c | ||
| xhci-mem.c | ||
| xhci-pci.c | ||
| xhci-ring.c | ||
| xhci.c | ||
| xhci.h | ||