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Date: Wed, 22 Jun 2011 10:30:45 -0700
From: matt mooney <mfm@...eddisk.com>
To: Kirill Smelkov <kirr@....spb.ru>
Cc: linux-usb@...r.kernel.org, Greg Kroah-Hartman <gregkh@...e.de>,
linux-uvc-devel@...ts.berlios.de, linux-media@...r.kernel.org,
linux-kernel@...r.kernel.org,
Alan Stern <stern@...land.harvard.edu>
Subject: Re: [RFC, PATCH] USB: EHCI: Allow users to override 80% max periodic bandwidth
On 20:02 Wed 22 Jun , Kirill Smelkov wrote:
> 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.
There is nothing arbitrary about 80%. The USB 2.0 Specification constrains
periodic transfers for high-speed endpoints to 80% of the microframe. See
section 5.6.4.
-mfm
> 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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