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Old 03-19-2012, 01:53 PM
Stefan Bader
 
Default ACK w/cmnt: USB: EHCI: go back to using the system clock for QH unlinks

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On 18.03.2012 10:23, Ming Lei wrote:
> From b75858acae39d4ed518bf82d4d03a6b9f685dc81 Mon Sep 17 00:00:00 2001
> From: Alan Stern <stern@rowland.harvard.edu> Date: Tue, 5 Jul 2011 12:34:05
> -0400 Subject: [PATCH] USB: EHCI: go back to using the system clock for QH
> unlinks
>
> BugLink: http://bugs.launchpad.net/bugs/624510
>
> This is a backport of commit
> 004c19682884d4f40000ce1ded53f4a1d0b18206(upstream) .

While not incorrect, the two lines may be documenting the flow of the patch
better when in the sob block.

>
> This patch (as1477) fixes a problem affecting a few types of EHCI
> controller. Contrary to what one might expect, these controllers
> automatically stop their internal frame counter when no ports are enabled.
> Since ehci-hcd currently relies on the frame counter for determining when
> it should unlink QHs from the async schedule, those controllers run into
> trouble: The frame counter stops and the QHs never get unlinked.
>
> Some systems have also experienced other problems traced back to commit
> b963801164618e25fbdc0cd452ce49c3628b46c8 (USB: ehci-hcd unlink speedups),
> which made the original switch from using the system clock to using the
> frame counter. It never became clear what the reason was for these
> problems, but evidently it is related to use of the frame counter.
>
> To fix all these problems, this patch more or less reverts that commit and
> goes back to using the system clock. But this can't be done cleanly
> because other changes have since been made to the scan_async() subroutine.
> One of these changes involved the tricky logic that tries to avoid
> rescanning QHs that have already been seen when the scanning loop is
> restarted, which happens whenever an URB is given back. Switching back to
> clock-based unlinks would make this logic even more complicated.
>
> Therefore the new code doesn't rescan the entire async list whenever a
> giveback occurs. Instead it rescans only the current QH and continues on
> from there. This requires the use of a separate pointer to keep track of
> the next QH to scan, since the current QH may be unlinked while the
> scanning is in progress. That new pointer must be global, so that it can
> be adjusted forward whenever the _next_ QH gets unlinked. (uhci-hcd uses
> this same trick.)
>
> Simplification of the scanning loop removes a level of indentation, which
> accounts for the size of the patch. The amount of code changed is
> relatively small, and it isn't exactly a reversion of the b963801164
> commit.
>
> This fixes Bugzilla #624510.
>
> Signed-off-by: Alan Stern <stern@rowland.harvard.edu>

The upstream patch has a Cc to stable here. This should not get dropped:
CC: <stable@kernel.org>

> Tested-by: Matej Kenda <matejken@gmail.com> Signed-off-by: Greg
> Kroah-Hartman <gregkh@suse.de>

BugLink: http://bugs.launchpad.net/bugs/624510

(backported from 004c19682884d4f40000ce1ded53f4a1d0b18206 upstream)
Signed-off-by: Ming Lei <ming.lei@canonical.com>

> --- drivers/usb/host/ehci-hcd.c | 8 ++--- drivers/usb/host/ehci-q.c |
> 82 +++++++++++++++++++++---------------------- drivers/usb/host/ehci.h
> | 4 ++- 3 files changed, 46 insertions(+), 48 deletions(-)
>
> diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
> index 7b2e99c..8d17f780 100644 --- a/drivers/usb/host/ehci-hcd.c +++
> b/drivers/usb/host/ehci-hcd.c @@ -84,7 +84,8 @@ static const char hcd_name
> [] = "ehci_hcd"; #define EHCI_IAA_MSECS 10 /* arbitrary */ #define
> EHCI_IO_JIFFIES (HZ/10) /* io watchdog > irq_thresh */ #define
> EHCI_ASYNC_JIFFIES (HZ/20) /* async idle timeout */ -#define
> EHCI_SHRINK_FRAMES 5 /* async qh unlink delay */ +#define
> EHCI_SHRINK_JIFFIES (DIV_ROUND_UP(HZ, 200) + 1) + /* 200-ms async qh
> unlink delay */
>
> /* Initial IRQ latency: faster than hw default */ static int
> log2_irq_thresh = 0; // 0 to 6 @@ -139,10 +140,7 @@ timer_action(struct
> ehci_hcd *ehci, enum ehci_timer_action action) break; /* case
> TIMER_ASYNC_SHRINK: */ default: - /* add a jiffie since we synch against
> the - * 8 KHz uframe counter. - */ - t =
> DIV_ROUND_UP(EHCI_SHRINK_FRAMES * HZ, 1000) + 1; + t =
> EHCI_SHRINK_JIFFIES; break; } mod_timer(&ehci->watchdog, t + jiffies); diff
> --git a/drivers/usb/host/ehci-q.c b/drivers/usb/host/ehci-q.c index
> 0ee5b4b..3b8fa18 100644 --- a/drivers/usb/host/ehci-q.c +++
> b/drivers/usb/host/ehci-q.c @@ -1204,6 +1204,8 @@ static void
> start_unlink_async (struct ehci_hcd *ehci, struct ehci_qh *qh)
>
> prev->hw->hw_next = qh->hw->hw_next; prev->qh_next = qh->qh_next; + if
> (ehci->qh_scan_next == qh) + ehci->qh_scan_next = qh->qh_next.qh; wmb ();
>
> /* If the controller isn't running, we don't have to wait for it */ @@
> -1229,53 +1231,49 @@ static void scan_async (struct ehci_hcd *ehci) struct
> ehci_qh *qh; enum ehci_timer_action action = TIMER_IO_WATCHDOG;
>
> - ehci->stamp = ehci_readl(ehci, &ehci->regs->frame_index);
> timer_action_done (ehci, TIMER_ASYNC_SHRINK); -rescan: stopped =
> !HC_IS_RUNNING(ehci_to_hcd(ehci)->state); - qh = ehci->async->qh_next.qh; -
> if (likely (qh != NULL)) { - do { - /* clean any finished work for this
> qh */ - if (!list_empty(&qh->qtd_list) && (stopped || - qh->stamp !=
> ehci->stamp)) { - int temp; - - /* unlinks could happen here;
> completion - * reporting drops the lock. rescan using - * the
> latest schedule, but don't rescan - * qhs we already finished (no
> looping) - * unless the controller is stopped. - */ - qh =
> qh_get (qh); - qh->stamp = ehci->stamp; - temp = qh_completions
> (ehci, qh); - if (qh->needs_rescan) - unlink_async(ehci, qh); -
> qh_put (qh); - if (temp != 0) { - goto rescan; - } - }
>
> - /* unlink idle entries, reducing DMA usage as well - * as HCD
> schedule-scanning costs. delay for any qh - * we just scanned, there's
> a not-unusual case that it - * doesn't stay idle for long. - * (plus,
> avoids some kind of re-activation race.) + ehci->qh_scan_next =
> ehci->async->qh_next.qh; + while (ehci->qh_scan_next) { + qh =
> ehci->qh_scan_next; + ehci->qh_scan_next = qh->qh_next.qh; + rescan: + /*
> clean any finished work for this qh */ + if (!list_empty(&qh->qtd_list))
> { + int temp; + + /* + * Unlinks could happen here; completion
> reporting + * drops the lock. That's why ehci->qh_scan_next + *
> always holds the next qh to scan; if the next qh + * gets unlinked then
> ehci->qh_scan_next is adjusted + * in start_unlink_async(). */ - if
> (list_empty(&qh->qtd_list) - && qh->qh_state == QH_STATE_LINKED) { -
> if (!ehci->reclaim && (stopped || - ((ehci->stamp - qh->stamp) &
> 0x1fff) - >= EHCI_SHRINK_FRAMES * 8)) - start_unlink_async(ehci,
> qh); - else - action = TIMER_ASYNC_SHRINK; - } + qh =
> qh_get(qh); + temp = qh_completions(ehci, qh); + if (qh->needs_rescan)
> + unlink_async(ehci, qh); + qh->unlink_time = jiffies +
> EHCI_SHRINK_JIFFIES; + qh_put(qh); + if (temp != 0) + goto rescan; +
> }
>
> - qh = qh->qh_next.qh; - } while (qh); + /* unlink idle entries,
> reducing DMA usage as well + * as HCD schedule-scanning costs. delay for
> any qh + * we just scanned, there's a not-unusual case that it + *
> doesn't stay idle for long. + * (plus, avoids some kind of re-activation
> race.) + */ + if (list_empty(&qh->qtd_list) + && qh->qh_state ==
> QH_STATE_LINKED) { + if (!ehci->reclaim && (stopped || +
> time_after_eq(jiffies, qh->unlink_time))) + start_unlink_async(ehci,
> qh); + else + action = TIMER_ASYNC_SHRINK; + } } if (action ==
> TIMER_ASYNC_SHRINK) timer_action (ehci, TIMER_ASYNC_SHRINK); diff --git
> a/drivers/usb/host/ehci.h b/drivers/usb/host/ehci.h index 5b3ca74..ad8a65e
> 100644 --- a/drivers/usb/host/ehci.h +++ b/drivers/usb/host/ehci.h @@ -74,6
> +74,7 @@ struct ehci_hcd { /* one per controller */ /* async schedule
> support */ struct ehci_qh *async; struct ehci_qh *reclaim; + struct
> ehci_qh *qh_scan_next; unsigned scanning : 1;
>
> /* periodic schedule support */ @@ -116,7 +117,7 @@ struct ehci_hcd { /*
> one per controller */ struct timer_list iaa_watchdog; struct timer_list
> watchdog; unsigned long actions; - unsigned stamp; + unsigned
> periodic_stamp; unsigned random_frame; unsigned long next_statechange;
> ktime_t last_periodic_enable; @@ -335,6 +336,7 @@ struct ehci_qh { struct
> ehci_qh *reclaim; /* next to reclaim */
>
> struct ehci_hcd *ehci; + unsigned long unlink_time;
>
> /* * Do NOT use atomic operations for QH refcounting. On some CPUs

Ok, looks to be like the upstream change. It was deemed stable material, too.
But either because it did not apply or because it went into the black whole of
what is the old stable@kernel.org address.

Acked-by: Stefan Bader <stefan.bader@canonical.com>
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