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Date: Wed, 22 Jun 2011 20:02:47 +0400
From: Kirill Smelkov <kirr@....spb.ru>
To: linux-usb@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...e.de>,
linux-uvc-devel@...ts.berlios.de, linux-media@...r.kernel.org,
linux-kernel@...r.kernel.org, Kirill Smelkov <kirr@....spb.ru>,
Alan Stern <stern@...land.harvard.edu>
Subject: [RFC, PATCH] 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% seems to be chosen pretty arbitrary to me, just
to serve as a reasonable default.
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.
Signed-off-by: Kirill Smelkov <kirr@....spb.ru>
Cc: Alan Stern <stern@...land.harvard.edu>
---
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");
+
#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);
+
+ /*
* 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)
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 = 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))
+ > (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 = 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 = uframe_periodic_max - stream->c_usecs;
do {
tmp = 1 << uf;
tmp <<= 8;
--
1.7.6.rc1
--
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