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Subject[PATCH v4 2/2] USB: EHCI: Allow users to override 80% max periodic bandwidth
Date
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>
---
Documentation/ABI/testing/sysfs-module | 23 +++++++
Documentation/usb/ehci.txt | 2 +
drivers/usb/host/ehci-hcd.c | 6 ++
drivers/usb/host/ehci-sched.c | 17 ++---
drivers/usb/host/ehci-sysfs.c | 104 ++++++++++++++++++++++++++++++-
drivers/usb/host/ehci.h | 2 +
6 files changed, 140 insertions(+), 14 deletions(-)
diff --git a/Documentation/ABI/testing/sysfs-module b/Documentation/ABI/testing/sysfs-module
index cfcec3b..9489ea8 100644
--- a/Documentation/ABI/testing/sysfs-module
+++ b/Documentation/ABI/testing/sysfs-module
@@ -10,3 +10,26 @@ KernelVersion: 2.6.35
Contact: masa-korg@dsn.okisemi.com
Description: Write/read Option ROM data.

+
+What: /sys/module/ehci_hcd/drivers/.../uframe_periodic_max
+Date: July 2011
+KernelVersion: 3.1
+Contact: Kirill Smelkov <kirr@mns.spb.ru>
+Description: Maximum time allowed for periodic transfers per microframe (μs)
+
+ [ USB 2.0 sets maximum allowed time for periodic transfers per
+ microframe to be 80%, that is 100 microseconds out of 125
+ microseconds (full microframe).
+
+ However there are cases, when 80% max isochronous bandwidth is
+ too limiting. For example two video streams could require 110
+ microseconds of isochronous bandwidth per microframe to work
+ together. ]
+
+ Through this setting it is possible to raise the limit so that
+ the host controller would allow allocating more than 100
+ microseconds of periodic bandwidth per microframe.
+
+ Beware, non-standard modes are usually not thoroughly tested by
+ hardware designers, and the hardware can malfunction when this
+ setting differ from default 100.
diff --git a/Documentation/usb/ehci.txt b/Documentation/usb/ehci.txt
index 9dcafa7..160bd6c 100644
--- a/Documentation/usb/ehci.txt
+++ b/Documentation/usb/ehci.txt
@@ -210,3 +210,5 @@ TBD: Interrupt and ISO transfer performance issues. Those periodic
transfers are fully scheduled, so the main issue is likely to be how
to trigger "high bandwidth" modes.

+TBD: More than standard 80% periodic bandwidth allocation is possible
+through sysfs uframe_periodic_max parameter. Describe that.
diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index 8306155..4ee62be 100644
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -572,6 +572,12 @@ static int ehci_init(struct usb_hcd *hcd)
hcc_params = ehci_readl(ehci, &ehci->caps->hcc_params);

/*
+ * by default set standard 80% (== 100 usec/uframe) max periodic
+ * bandwidth as required by USB 2.0
+ */
+ ehci->uframe_periodic_max = 100;
+
+ /*
* 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 6c9fbe3..2abf854 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 > ehci->uframe_periodic_max)
ehci_err (ehci, "uframe %d sched overrun: %d usecs\n",
frame * 8 + uframe, usecs);
#endif
@@ -709,11 +709,8 @@ static int check_period (
if (uframe >= 8)
return 0;

- /*
- * 80% periodic == 100 usec/uframe available
- * convert "usecs we need" to "max already claimed"
- */
- usecs = 100 - usecs;
+ /* convert "usecs we need" to "max already claimed" */
+ usecs = ehci->uframe_periodic_max - usecs;

/* we "know" 2 and 4 uframe intervals were rejected; so
* for period 0, check _every_ microframe in the schedule.
@@ -1286,9 +1283,9 @@ itd_slot_ok (
{
uframe %= period;
do {
- /* can't commit more than 80% periodic == 100 usec */
+ /* can't commit more than uframe_periodic_max usec */
if (periodic_usecs (ehci, uframe >> 3, uframe & 0x7)
- > (100 - usecs))
+ > (ehci->uframe_periodic_max - usecs))
return 0;

/* we know urb->interval is 2^N uframes */
@@ -1345,7 +1342,7 @@ sitd_slot_ok (
#endif

/* check starts (OUT uses more than one) */
- max_used = 100 - stream->usecs;
+ max_used = ehci->uframe_periodic_max - stream->usecs;
for (tmp = stream->raw_mask & 0xff; tmp; tmp >>= 1, uf++) {
if (periodic_usecs (ehci, frame, uf) > max_used)
return 0;
@@ -1354,7 +1351,7 @@ sitd_slot_ok (
/* for IN, check CSPLIT */
if (stream->c_usecs) {
uf = uframe & 7;
- max_used = 100 - stream->c_usecs;
+ max_used = ehci->uframe_periodic_max - stream->c_usecs;
do {
tmp = 1 << uf;
tmp <<= 8;
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 ssize_t store_companion(struct device *dev,
}
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);
}
diff --git a/drivers/usb/host/ehci.h b/drivers/usb/host/ehci.h
index bd6ff48..fa3129f 100644
--- a/drivers/usb/host/ehci.h
+++ b/drivers/usb/host/ehci.h
@@ -87,6 +87,8 @@ struct ehci_hcd { /* one per controller */
union ehci_shadow *pshadow; /* mirror hw periodic table */
int next_uframe; /* scan periodic, start here */
unsigned periodic_sched; /* periodic activity count */
+ unsigned uframe_periodic_max; /* max periodic time per uframe */
+

/* list of itds & sitds completed while clock_frame was still active */
struct list_head cached_itd_list;
--
1.7.6.rc3
--
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