USB: EHCI: Allow users to override 80% max periodic bandwidth
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>
diff --git a/drivers/usb/host/ehci-sysfs.c b/drivers/usb/host/ehci-sysfs.c
index 29824a9..14ced00 100644
--- a/drivers/usb/host/ehci-sysfs.c
+++ b/drivers/usb/host/ehci-sysfs.c
@@ -74,21 +74,117 @@
}
static DEVICE_ATTR(companion, 0644, show_companion, store_companion);
+
+/*
+ * Display / Set uframe_periodic_max
+ */
+static ssize_t show_uframe_periodic_max(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ struct ehci_hcd *ehci;
+ int n;
+
+ ehci = hcd_to_ehci(bus_to_hcd(dev_get_drvdata(dev)));
+ n = scnprintf(buf, PAGE_SIZE, "%d\n", ehci->uframe_periodic_max);
+ return n;
+}
+
+
+static ssize_t store_uframe_periodic_max(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct ehci_hcd *ehci;
+ unsigned uframe_periodic_max;
+ unsigned frame, uframe;
+ unsigned short allocated_max;
+ unsigned long flags;
+ ssize_t ret;
+
+ ehci = hcd_to_ehci(bus_to_hcd(dev_get_drvdata(dev)));
+ if (kstrtouint(buf, 0, &uframe_periodic_max) < 0)
+ return -EINVAL;
+
+ if (uframe_periodic_max < 100 || uframe_periodic_max >= 125) {
+ ehci_info(ehci, "rejecting invalid request for "
+ "uframe_periodic_max=%u\n", uframe_periodic_max);
+ return -EINVAL;
+ }
+
+ ret = -EINVAL;
+
+ /*
+ * lock, so that our checking does not race with possible periodic
+ * bandwidth allocation through submitting new urbs.
+ */
+ spin_lock_irqsave (&ehci->lock, flags);
+
+ /*
+ * for request to decrease max periodic bandwidth, we have to check
+ * every microframe in the schedule to see whether the decrease is
+ * possible.
+ */
+ if (uframe_periodic_max < ehci->uframe_periodic_max) {
+ allocated_max = 0;
+
+ for (frame = 0; frame < ehci->periodic_size; ++frame)
+ for (uframe = 0; uframe < 7; ++uframe)
+ allocated_max = max(allocated_max,
+ periodic_usecs (ehci, frame, uframe));
+
+ if (allocated_max > uframe_periodic_max) {
+ ehci_info(ehci,
+ "cannot decrease uframe_periodic_max becase "
+ "periodic bandwidth is already allocated "
+ "(%u > %u)\n",
+ allocated_max, uframe_periodic_max);
+ goto out_unlock;
+ }
+ }
+
+ /* increasing is always ok */
+
+ ehci_info(ehci, "setting max periodic bandwidth to %u%% "
+ "(== %u usec/uframe)\n",
+ 100*uframe_periodic_max/125, uframe_periodic_max);
+
+ if (uframe_periodic_max != 100)
+ ehci_warn(ehci, "max periodic bandwidth set is non-standard\n");
+
+ ehci->uframe_periodic_max = uframe_periodic_max;
+ ret = count;
+
+out_unlock:
+ spin_unlock_irqrestore (&ehci->lock, flags);
+ return ret;
+}
+static DEVICE_ATTR(uframe_periodic_max, 0644, show_uframe_periodic_max, store_uframe_periodic_max);
+
+
static inline int create_sysfs_files(struct ehci_hcd *ehci)
{
+ struct device *controller = ehci_to_hcd(ehci)->self.controller;
int i = 0;
/* with integrated TT there is no companion! */
if (!ehci_is_TDI(ehci))
- i = device_create_file(ehci_to_hcd(ehci)->self.controller,
- &dev_attr_companion);
+ i = device_create_file(controller, &dev_attr_companion);
+ if (i)
+ goto out;
+
+ i = device_create_file(controller, &dev_attr_uframe_periodic_max);
+out:
return i;
}
static inline void remove_sysfs_files(struct ehci_hcd *ehci)
{
+ struct device *controller = ehci_to_hcd(ehci)->self.controller;
+
/* with integrated TT there is no companion! */
if (!ehci_is_TDI(ehci))
- device_remove_file(ehci_to_hcd(ehci)->self.controller,
- &dev_attr_companion);
+ device_remove_file(controller, &dev_attr_companion);
+
+ device_remove_file(controller, &dev_attr_uframe_periodic_max);
}