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>

4 files changed, 115 insertions, 14 deletions

diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index 8306155de9e5..4ee62bef3723 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 6c9fbe352f73..2abf8543f083 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 29824a98aec9..14ced00ba220 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 bd6ff489baf9..fa3129fe1ee0 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;