[PATCH] serial: PL011: clear pending interrupts

[Linus Walleij]

On Mon, Mar 12, 2012 at 11:11 AM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:

>> > +   /* RXIS but RXFE? Just clear the interrupt */
>> > +   if(unlikely(fifotaken == 0))
>> > +           writew(UART011_RTIS | UART011_RXIS,
>> > +                  uap->port.membase + UART011_ICR);
>
> BTW, I don't see why we need any of this stuff.
>
> The problem as described is that the interrupt handler is called with one
> of the receive flags set (UART011_RTIS or UART011_RXIS) but with
> UART01x_FR_RXFE clear.
>
> The problem report indicates that this is caused when we switch from FIFO
> mode to non-FIFO mode, and the FIFO contained some unread characters.
>
> That can only happen once we've enabled interrupts in the IMSC register,
> which doesn't happen until later in the startup function.
>
> So:
>
>        spin_lock_irq(&uap->port.lock);
>        uap->im = UART011_RTIM;
>        if (!pl011_dma_rx_running(uap))
>                uap->im |= UART011_RXIM;
>        writew(uap->im, uap->port.membase + UART011_IMSC);
>        spin_unlock_irq(&uap->port.lock);
>
> clearing the transmit/receive interrupts here _before_ we unmask them
> should be sufficient.

Right! OK I'll cook a v2 patch according to this suggestion and
request Chanho to test it.

Yours,
Linus Walleij