From a1d5ce866f2e2062246343af757c22e9abe4e844 Mon Sep 17 00:00:00 2001 From: Jonathan Bell 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 --- 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 @@ -301,6 +301,7 @@ static void xhci_pci_quirks(struct devic xhci->quirks |= XHCI_LPM_SUPPORT; xhci->quirks |= XHCI_EP_CTX_BROKEN_DCS; 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 @@ -1905,6 +1905,7 @@ struct xhci_hcd { #define XHCI_BROKEN_D3COLD BIT_ULL(41) #define XHCI_EP_CTX_BROKEN_DCS BIT_ULL(42) #define XHCI_AVOID_DQ_ON_LINK BIT_ULL(43) +#define XHCI_VLI_TRB_CACHE_BUG BIT_ULL(44) unsigned int num_active_eps; unsigned int limit_active_eps;