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    SubjectRe: [PATCHv2] musb_host: fix lockup on rxcsr_h_error
    Hi,

    On Wed, Apr 27, 2016 at 09:51:58AM +0300, Max Uvarov wrote:
    > Fix soft lockup when resetting remote device attached
    > to usb host. Configuration:
    > pppd -> musb hub -> usb-serial -> gsm modem

    I have heard a few reports similar to this symptom, but never been able
    to reproduce it on my side.

    > When gsm modem resets, musb rolls in incoming rx interrupts
    > which does not give any time to other application as result
    > it totally lock ups. Solution is to keep original logic for RXCSR_H_ERROR

    Have you looked where exact place in the interrupt routine the execution
    has stuck in?

    > and merge RXCSR_DATAERROR and RXCSR_H_ERROR branches to call same code
    > for setting rx stall with MUSB_RXCSR_H_WZC_BITS.

    MUSB_RXCSR_H_WZC_BITS itself does not set rx stall, it just ensures
    MUSB_RXCSR_H_RXSTALL not to be cleared. Please check its comment in
    musb_regs.h.

    >
    > Signed-off-by: Max Uvarov <muvarov@gmail.com>
    > ---
    > v2: use bitwise or for error flags before logical and. (Sergei Shtylyov).
    >
    > drivers/usb/musb/musb_host.c | 12 +++++-------
    > 1 file changed, 5 insertions(+), 7 deletions(-)
    >
    > diff --git a/drivers/usb/musb/musb_host.c b/drivers/usb/musb/musb_host.c
    > index c3d5fc9..2d9aa78 100644
    > --- a/drivers/usb/musb/musb_host.c
    > +++ b/drivers/usb/musb/musb_host.c
    > @@ -1592,14 +1592,12 @@ void musb_host_rx(struct musb *musb, u8 epnum)

    What kernel do you use? This line # is away off from upstream kernel.

    >
    > /* stall; record URB status */
    > status = -EPIPE;
    > + } else if (rx_csr & (MUSB_RXCSR_DATAERROR | MUSB_RXCSR_H_ERROR)) {
    >
    > - } else if (rx_csr & MUSB_RXCSR_H_ERROR) {
    > - dev_dbg(musb->controller, "end %d RX proto error\n", epnum);
    > -
    > - status = -EPROTO;
    > - musb_writeb(epio, MUSB_RXINTERVAL, 0);
    > -
    > - } else if (rx_csr & MUSB_RXCSR_DATAERROR) {
    > + if (rx_csr & MUSB_RXCSR_H_ERROR) {
    > + status = -EPROTO;
    > + musb_writeb(epio, MUSB_RXINTERVAL, 0);
    > + }

    Please help me to understand how this change fixes the issue. I see the
    most effect of the change here is directly 'goto finish' so that 'done'
    flag is not set, then musb_advance_schedule() is not called. Is this the
    case or I missed other important pieces?

    Thanks,
    -Bin.

    >
    > if (USB_ENDPOINT_XFER_ISOC != qh->type) {
    > dev_dbg(musb->controller, "RX end %d NAK timeout\n", epnum);
    > --
    > 1.9.1
    >
    > --
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