Re: [PATCH] amba-pl011: clear previous interrupts before request_irq

Russell King
2012-01-18T10:16:09Z

On Wed, Jan 18, 2012 at 03:34:11PM +0530, Shreshtha Kumar SAHU wrote:
>
> >From 0742fc49405b2a6f562981f61d93198e1595f30d Mon Sep 17 00:00:00 2001
> From: Shreshtha Kumar Sahu <shreshthakumar.sahu@stericsson.com>
> Date: Tue, 17 Jan 2012 12:23:19 +0530
> Subject: [PATCH v2] amba-pl011: clear previous interrupts before request_irq
>
> All previous interrupts should be cleared before installing
> interrupt handler i.e. before request_irq. pl011_shutdown
> clears the interrupt register but there may be case where
> bootloader transfers control to kernel and there are some
> pending interrupts. In this case interrupt handler will get
> called even before interrupt mask is enabled.
>
> Acked-by: Linus Walleij <linus.walleij@linaro.org>

No sign-off, and I don't understand the problem being aluded to in the
description above - particularly the last sentence.

In theory, we should be prepared for the interrupt handler to be called
immediately after request_irq() returns, and not have the driver misbehave
because of that. Maybe a better solution would be to move request_irq()
a bit later?

But first, having a clearer description of the problem you're seeing
would be beneficial.

> ---
> drivers/tty/serial/amba-pl011.c | 9 +++++++++
> 1 files changed, 9 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
> index 6958594..6dafaa2 100644
> --- a/drivers/tty/serial/amba-pl011.c
> +++ b/drivers/tty/serial/amba-pl011.c
> @@ -1381,6 +1381,15 @@ static int pl011_startup(struct uart_port *port)
> uap->port.uartclk = clk_get_rate(uap->clk);
>
> /*
> + * Clear previous interrupts before installing interrupt handler
> + */
> + spin_lock_irq(&uap->port.lock);
> + uap->im = 0;
> + writew(uap->im, uap->port.membase + UART011_IMSC);
> + writew(0xffff, uap->port.membase + UART011_ICR);
> + spin_unlock_irq(&uap->port.lock);
> +
> + /*
> * Allocate the IRQ
> */
> retval = request_irq(uap->port.irq, pl011_int, 0, "uart-pl011", uap);
> --
> 1.7.4.3
>

--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/