• Sarah Sharp's avatar
    xhci: Fix command ring replay after resume. · 89821320
    Sarah Sharp authored
    Andiry's xHCI bus suspend patch introduced the possibly of a host
    controller replaying old commands on the command ring, if the host
    successfully restores the registers after a resume.
    
    After a resume from suspend, the xHCI driver must restore the registers,
    including the command ring pointer.  I had suggested that Andiry set the
    command ring pointer to the current command ring dequeue pointer, so that
    the driver wouldn't have to zero the command ring.
    
    Unfortunately, setting the command ring pointer to the current dequeue
    pointer won't work because the register assumes the pointer is 64-byte
    aligned, and TRBs on the command ring are 16-byte aligned.  The lower
    seven bits will always be masked off, leading to the written pointer being
    up to 3 TRBs behind the intended pointer.
    
    Here's a log excerpt.  On init, the xHCI driver places a vendor-specific
    command on the command ring:
    
    [  215.750958] xhci_hcd 0000:01:00.0: Vendor specific event TRB type = 48
    [  215.750960] xhci_hcd 0000:01:00.0: NEC firmware version 30.25
    [  215.750962] xhci_hcd 0000:01:00.0: Command ring deq = 0x3781e010 (DMA)
    
    When we resume, the command ring dequeue pointer to be written should have
    been 0x3781e010.  Instead, it's 0x3781e000:
    
    [  235.557846] xhci_hcd 0000:01:00.0: // Setting command ring address to 0x3781e001
    [  235.557848] xhci_hcd 0000:01:00.0: `MEM_WRITE_DWORD(3'b000, 64'hffffc900100bc038, 64'h3781e001, 4'hf);
    [  235.557850] xhci_hcd 0000:01:00.0: `MEM_WRITE_DWORD(3'b000, 32'hffffc900100bc020, 32'h204, 4'hf);
    [  235.557866] usb usb9: root hub lost power or was reset
    
    (I can't see the results of this bug because the xHCI restore always fails
    on this box, and the xHCI driver re-allocates everything.)
    
    The fix is to zero the command ring and put the software and hardware
    enqueue and dequeue pointer back to the beginning of the ring.  We do this
    before the system suspends, to be paranoid and prevent the BIOS from
    starting the host without clearing the command ring pointer, which might
    cause the host to muck with stale memory.  (The pointer isn't required to
    be in the suspend power well, but it could be.)  The command ring pointer
    is set again after the host resumes.
    Signed-off-by: default avatarSarah Sharp <sarah.a.sharp@linux.intel.com>
    Tested-by: default avatarAndiry Xu <andiry.xu@amd.com>
    89821320
xhci.c 82.2 KB