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    SubjectRe: [PATCH 3/3] 8250: add workaround for MPC8[356]xx UART break IRQ storm
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    On Thu, Dec 1, 2011 at 7:57 PM, Alan Cox <alan@linux.intel.com> wrote:
    >
    >> @@ -1553,7 +1554,15 @@ static void serial8250_handle_port(struct
    >> uart_8250_port *up)
    >>       spin_lock_irqsave(&up->port.lock, flags);
    >>
    >> -     status = serial_inp(up, UART_LSR);
    >> +     /* Workaround for IRQ storm errata on break with Freescale
    >> 16550 */
    >> +     if (UART_BUG_FSLBK & up->port.bugs && up->lsr_last &
    >> UART_LSR_BI) {
    >> +             up->lsr_last &= ~UART_LSR_BI;
    >> +             serial_inp(up, UART_RX);
    >> +             spin_unlock_irqrestore(&up->port.lock, flags);
    >> +             return;
    >> +     }
    >> +
    >> +     status = up->lsr_last = serial_inp(up, UART_LSR);
    >
    > We've now had a recent pile of IRQ function changes adding more quirk
    > bits and special casing. This doesn't scale. We either need to make
    > handle_port a method the specific drivers can override or you could
    > hide the mess in your serial_inp implementation and not touch any core
    > code.

    To be fair, this one is zero cost for !PPC, but I understand your point,
    and the idea of hiding it somehow in serial_inp was something that
    never crossed my mind. I'll look into seeing if I can abuse that.

    >
    > I really don't mind which but I suspect dealing with it in your
    > serial_inp handler so that when you read UART_LSR you do the fixup
    > might be simplest providing you can just do that.
    >
    > Sorting out a ->handle_port override is probably ultimately the right
    > thing to do and then we can push some of the other funnies out further.
    >
    > At this point it's becoming increasingly clear that 8250 UART cloners
    > are both very bad at cloning the things accurately, and very busy adding
    > extra useful features so we need to start to treat 8250.c as a library
    > you can wrap.

    Sad but true. It is like a time warp back to lib8390.c --- whee.

    P.

    >
    > Alan
    > --
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