Kernel 6.1 backport of Renesas interrupt storm fix #169
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iluminat23
approved these changes
Sep 12, 2023
commit 32297b0849a94a9b6ef0eb7bae4a41c353572c40 upstream. The Event Handler Busy bit shall be cleared by software when the Event Ring is empty. The xHC is thereby informed that it may raise another interrupt once it has enqueued new events (sec 4.17.2). However since commit dc0ffbe ("usb: host: xhci: update event ring dequeue pointer on purpose"), the EHB bit is already cleared after half a segment has been processed. As a result, spurious interrupts may occur: - xhci_irq() processes half a segment, clears EHB, continues processing remaining events. - xHC enqueues new events. Because EHB has been cleared, xHC sets Interrupt Pending bit. Interrupt moderation countdown begins. - Meanwhile xhci_irq() continues processing events. Interrupt moderation countdown reaches zero, so an MSI interrupt is signaled. - xhci_irq() empties the Event Ring, clears EHB again and is done. - Because an MSI interrupt has been signaled, xhci_irq() is run again. It discovers there's nothing to do and returns IRQ_NONE. Avoid by clearing the EHB bit only at the end of xhci_irq(). Fixes: dc0ffbe ("usb: host: xhci: update event ring dequeue pointer on purpose") Signed-off-by: Lukas Wunner <lukas@wunner.de> Cc: stable@vger.kernel.org # v5.5+ Cc: Peter Chen <peter.chen@kernel.org>
commit 256a5264729face90cfb9d56e7ffda6bac3c249b upstream. When using more than one Event Ring segment (ERSTSZ > 1), software shall set the DESI bits in the ERDP register to the number of the segment to which the upper ERDP bits are pointing. The xHC may use the DESI bits as a shortcut to determine whether it needs to check for an Event Ring Full condition: If it's enqueueing events in a different segment, it need not compare its internal Enqueue Pointer with the Dequeue Pointer in the upper bits of the ERDP register (sec 5.5.2.3.3). Not setting the DESI bits correctly can result in the xHC enqueueing events past the Dequeue Pointer. On Renesas uPD720201 host controllers, incorrect DESI bits cause an interrupt storm. For comparison, VIA VL805 host controllers do not exhibit such problems. Perhaps they do not take advantage of the optimization afforded by the DESI bits. To fix the issue, assign the segment number to each struct xhci_segment in xhci_segment_alloc(). When advancing the Dequeue Pointer in xhci_update_erst_dequeue(), write the segment number to the DESI bits. On driver probe, set the DESI bits to zero in xhci_set_hc_event_deq() as processing starts in segment 0. Previously that function (incorrectly) treated the DESI bits as if they're declared RsvdP. Signed-off-by: Lukas Wunner <lukas@wunner.de>
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iluminat23
approved these changes
Sep 12, 2023
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Upstream commits queued for v6.7-rc1:
https://git.kernel.org/mnyman/xhci/c/32297b0849a9
https://git.kernel.org/mnyman/xhci/c/256a5264729f
In theory the sha1 hashes could change if the for-usb-next branch is rebased. Hopefully that doesn't happen.