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This patch takes advantage of block transfer interrupts on Intel XHCI controllers which is used during isochronous transfers. Because of a bug in hardware (see usb_host_isoc_bei.patch header), this feature has been disabled for Intel leading to up to 8000 interrupts/s for isochronous transfer causing severe CPU consumption on Genode. With this commit we lower host driver consumption to normal levels. issue #4149
108 lines
4.6 KiB
Diff
108 lines
4.6 KiB
Diff
For Intel host controllers an interrupt is raised for every isochronous packet,
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because of the "AVOID_BEI" quirk. The reasoning for this is found in the
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following commit:
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commit 227a4fd801c8a9fa2c4700ab98ec1aec06e3b44d
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Author: Lu Baolu <baolu.lu@linux.intel.com>
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Date: Mon Mar 23 18:27:42 2015 +0200
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usb: xhci: apply XHCI_AVOID_BEI quirk to all Intel xHCI controllers
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When a device with an isochronous endpoint is plugged into the Intel
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xHCI host controller, and the driver submits multiple frames per URB,
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the xHCI driver will set the Block Event Interrupt (BEI) flag on all
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but the last TD for the URB. This causes the host controller to place
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an event on the event ring, but not send an interrupt. When the last
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TD for the URB completes, BEI is cleared, and we get an interrupt for
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the whole URB.
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However, under Intel xHCI host controllers, if the event ring is full
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of events from transfers with BEI set, an "Event Ring is Full" event
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will be posted to the last entry of the event ring, but no interrupt
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is generated. Host will cease all transfer and command executions and
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wait until software completes handling the pending events in the event
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ring. That means xHC stops, but event of "event ring is full" is not
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notified. As the result, the xHC looks like dead to user.
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This patch is to apply XHCI_AVOID_BEI quirk to Intel xHC devices. And
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it should be backported to kernels as old as 3.0, that contains the
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commit 69e848c2090a ("Intel xhci: Support EHCI/xHCI port switching.").
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Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
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Tested-by: Alistair Grant <akgrant0710@gmail.com>
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Cc: stable@vger.kernel.org
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Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
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Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Because this behavior up to 8000 interrupts/s can be raised by the host
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controller during isochronous transfer. Since 2020 there exists a patch that
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relaxes this burden and which we will apply.
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Author: Mathias Nyman <mathias.nyman@linux.intel.com>
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Date: Fr Sep 18 2020 13:17:24 2020 +0200
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xhci: Tune interrupt blocking for isochronous transfers
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controllers with XHCI_AVOID_BEI quirk cause too frequent interrupts
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and affect power management.
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To avoid interrupting on every isochronous interval the BEI (Block
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Event Interrupt) flag is set for all except the last Isoch TRB in a URB.
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This lead to event ring filling up in case several isoc URB were
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queued and cancelled rapidly, which some controllers didn't
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handle well, and thus the XHCI_AVOID_BEI quirk was introduced.
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see commit 227a4fd801c8 ("usb: xhci: apply XHCI_AVOID_BEI quirk to all
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Intel xHCI controllers")
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With the XHCI_AVOID_BEI quirk each Isoch TRB will trigger an interrupt.
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This can cause up to 8000 interrupts per second for isochronous transfers
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with HD USB3 cameras, affecting power saving.
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The event ring fits 256 events, instead of interrupting on every
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isochronous TRB if XHCI_AVOID_BEI is set we make sure at least every
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8th Isochronous TRB asserts an interrupt, clearing the event ring.
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Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
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diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
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index 028891a..31f6bd3 100644
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--- a/drivers/usb/host/xhci-ring.c
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+++ b/drivers/usb/host/xhci-ring.c
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@@ -3608,6 +3608,24 @@ static int xhci_get_isoc_frame_id(struct xhci_hcd *xhci,
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return start_frame;
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}
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+/* Check if we should generate event interrupt for a TD in an isoc URB */
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+static bool trb_block_event_intr(struct xhci_hcd *xhci, int num_tds, int i)
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+{
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+ if (xhci->hci_version < 0x100)
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+ return false;
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+ /* always generate an event interrupt for the last TD */
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+ if (i == num_tds - 1)
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+ return false;
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+ /*
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+ * If AVOID_BEI is set the host handles full event rings poorly,
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+ * generate an event at least every 8th TD to clear the event ring
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+ */
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+ if (i && xhci->quirks & XHCI_AVOID_BEI)
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+ return !!(i % 8);
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+
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+ return true;
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+}
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+
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/* This is for isoc transfer */
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static int xhci_queue_isoc_tx(struct xhci_hcd *xhci, gfp_t mem_flags,
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struct urb *urb, int slot_id, unsigned int ep_index)
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@@ -3715,10 +3733,7 @@ static int xhci_queue_isoc_tx(struct xhci_hcd *xhci, gfp_t mem_flags,
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more_trbs_coming = false;
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td->last_trb = ep_ring->enqueue;
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field |= TRB_IOC;
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- /* set BEI, except for the last TD */
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- if (xhci->hci_version >= 0x100 &&
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- !(xhci->quirks & XHCI_AVOID_BEI) &&
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- i < num_tds - 1)
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+ if (trb_block_event_intr(xhci, num_tds, i))
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field |= TRB_BEI;
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}
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/* Calculate TRB length */
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