Hi Nicolas,

Thanks for the report.

On 02/09/2015 08:34 AM, Nicolas Schichan wrote:

On 09/10/2014 09:29 PM, Sebastian Andrzej Siewior wrote:

quoted

The serial8250_do_startup() function unconditionally clears the
interrupts and for that it reads from the RX-FIFO without checking if
there is a byte in the FIFO or not. This works fine on OMAP4+ HW like
AM335x or DRA7.
OMAP3630 ES1.1 (which means probably all OMAP3 and earlier) does not like
this:

Hello,

Sorry to wake up an old thread, but I'm affraid that this patch causes
problems on Marvell 88f6282 (Kirkwood).

When a caracter is received on the UART while the kernel is printing
the boot messages, as soon as the kernel configures the UART for
receiving (after root filesystem mount), it gets stuck printing the
following message repeatedly:

serial8250: too much work for irq29

Once stuck, the reception of another character allows the boot process
to finish.

From what I can gather, when we hit that, the UART_IIR_NO_INT is 0 (so the
interrupt is raised), but the UART_LSR_DR bit is 0 as well so the UART_RX
register is never read to clear the interrupt.

The "too much work" message means serial8250_handle_irq() is returning 0,
ie., not handled. Which in turn means IIR indicates no interrupt is pending
(UART_IIR_NO_INT == 1).

Can you log the register values for LSR and IIR at both patch locations
in serial8250_do_startup()?

(I can get you a debug patch, if necessary. Let me know)

Regards,
Peter Hurley

We are using the second UART multiplexed on mpps 15 and 16.

Reverting this particular patch fixes the issue.

We are seing the problem on a 3.18 kernel.