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- From 02b78815e793d3f778b3f9b199f17cdd7f7e074d Mon Sep 17 00:00:00 2001
- From: Jonathan Bell <[email protected]>
- Date: Mon, 13 Dec 2021 16:04:03 +0000
- Subject: [PATCH] usb: xhci: add VLI_TRB_CACHE_BUG quirk
- The VL805 fetches up to 4 transfer TRBs at a time. TRB reads don't cross
- a 64B boundary, and if a TRB is fetched and is not on a 64B boundary,
- the read is sized up to the next 64B boundary.
- However the VL805 implements a readahead prefetch for TRBs on a transfer
- ring. This fetches the next 64B after any TRB read has happened. Near
- the end of a ring segment, the prefetcher can read the first 64B of the
- next page in physical memory and this is where the behaviour causes a
- bug.
- The controller does not tag reads with which endpoint they are for, so
- if the start of the next page is a ring segment used by a victim
- endpoint, and the victim endpoint is about to fetch TRBs from the start
- of the segment, the victim endpoint will read from the prefetched data
- and not perform a read to main memory. If the data is stale, the ring
- cycle state bit may not be correct and the endpoint will silently halt.
- Adjust trbs_per_seg for transfer rings allocated for this controller.
- See https://github.com/raspberrypi/linux/issues/4685
- Signed-off-by: Jonathan Bell <[email protected]>
- ---
- drivers/usb/host/xhci-mem.c | 11 +++++++++++
- drivers/usb/host/xhci-pci.c | 1 +
- drivers/usb/host/xhci.h | 1 +
- 3 files changed, 13 insertions(+)
- --- a/drivers/usb/host/xhci-mem.c
- +++ b/drivers/usb/host/xhci-mem.c
- @@ -392,6 +392,17 @@ struct xhci_ring *xhci_ring_alloc(struct
- return ring;
-
- ring->trbs_per_seg = TRBS_PER_SEGMENT;
- + /*
- + * The Via VL805 has a bug where cache readahead will fetch off the end
- + * of a page if the Link TRB of a transfer ring is in the last 4 slots.
- + * Where there are consecutive physical pages containing ring segments,
- + * this can cause a desync between the controller's view of a ring
- + * and the host.
- + */
- + if (xhci->quirks & XHCI_VLI_TRB_CACHE_BUG &&
- + type != TYPE_EVENT && type != TYPE_COMMAND)
- + ring->trbs_per_seg -= 4;
- +
- ret = xhci_alloc_segments_for_ring(xhci, &ring->first_seg,
- &ring->last_seg, num_segs, ring->trbs_per_seg,
- cycle_state, type, max_packet, flags);
- --- a/drivers/usb/host/xhci-pci.c
- +++ b/drivers/usb/host/xhci-pci.c
- @@ -296,6 +296,7 @@ static void xhci_pci_quirks(struct devic
- if (pdev->vendor == PCI_VENDOR_ID_VIA && pdev->device == 0x3483) {
- xhci->quirks |= XHCI_LPM_SUPPORT;
- xhci->quirks |= XHCI_AVOID_DQ_ON_LINK;
- + xhci->quirks |= XHCI_VLI_TRB_CACHE_BUG;
- }
-
- if (pdev->vendor == PCI_VENDOR_ID_ASMEDIA &&
- --- a/drivers/usb/host/xhci.h
- +++ b/drivers/usb/host/xhci.h
- @@ -1904,6 +1904,7 @@ struct xhci_hcd {
- #define XHCI_ZHAOXIN_TRB_FETCH BIT_ULL(45)
- #define XHCI_ZHAOXIN_HOST BIT_ULL(46)
- #define XHCI_AVOID_DQ_ON_LINK BIT_ULL(47)
- +#define XHCI_VLI_TRB_CACHE_BUG BIT_ULL(48)
-
- unsigned int num_active_eps;
- unsigned int limit_active_eps;
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