[PATCH] iop13xx: workaround errata that causes uart interrupts to be missed

[Russell King - ARM Linux]

You need to cc Alan Cox and lkml on this.

On Thu, Oct 29, 2009 at 12:09:00PM -0700, Dan Williams wrote:
> Reading the uart iir register sometimes results in the interrupt being
> cleared without being reported.  Use the the system interrupt pending
> register as a fallback.
> 
> This converts locations in the code that only care about the interrupt
> pending bit to use the iir_int_status() macro.
> 
> Signed-off-by: Dan Williams <dan.j.williams at intel.com>
> ---
> This patch has been sitting in the 'misc' branch of the xscaleiop tree
> in an un-mergeable form for quite a while [1].  I finally got fed up
> with forward porting it and would like to try to get this workaround
> upstream.  There appears to be no maintainer for 8250.c, so not sure who
> should merge this.  I can append it to the end of my next pull request
> for the iop queue...?
> 
> Thanks,
> Dan
> 
> [1]: http://git.kernel.org/?p=linux/kernel/git/djbw/xscaleiop.git;a=commitdiff;h=a7d124f5
> 
>  drivers/serial/8250.c |   36 +++++++++++++++++++++++++++++++++---
>  1 files changed, 33 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
> index b1ae774..c905860 100644
> --- a/drivers/serial/8250.c
> +++ b/drivers/serial/8250.c
> @@ -547,6 +547,36 @@ serial_out_sync(struct uart_8250_port *up, int offset, int value)
>  	(up->port.serial_in(&(up)->port, (offset)))
>  #define serial_out(up, offset, value)	\
>  	(up->port.serial_out(&(up)->port, (offset), (value)))
> +
> +#ifndef CONFIG_ARCH_IOP13XX
> +#define iir_int_status(up) serial_in((up), UART_IIR)
> +#else
> +/* A silicon issue on IOP13XX causes IIR reads to return UART_IIR_NO_INT
> + * even if an interrupt is pending. Use the system interrupt pending
> + * register to check for servicing as a workaround.
> + */
> +#include <mach/irqs.h>
> +static unsigned int iir_int_status(struct uart_8250_port *up)
> +{
> +	unsigned long membase = (unsigned long) up->port.membase;
> +	unsigned long ipnd, iir;
> +
> +	ipnd = read_intpnd_1();
> +	iir = UART_IIR_NO_INT;
> +	if (membase == IOP13XX_UART0_VIRT) {
> +		if (ipnd & (1 << (IRQ_IOP13XX_UART0 - 32)))
> +			iir &= ~UART_IIR_NO_INT;
> +	} else if (membase == IOP13XX_UART1_VIRT) {
> +		if (ipnd & (1 << (IRQ_IOP13XX_UART1 - 32)))
> +			iir &= ~UART_IIR_NO_INT;
> +	} else
> +		BUG();
> +	/* clear the interupt via the LSR */
> +	mem_serial_in(&up->port, UART_LSR);
> +	return iir;
> +}
> +#endif
> +
>  /*
>   * We used to support using pause I/O for certain machines.  We
>   * haven't supported this for a while, but just in case it's badly
> @@ -1572,7 +1602,7 @@ static irqreturn_t serial8250_interrupt(int irq, void *dev_id)
>  
>  		up = list_entry(l, struct uart_8250_port, list);
>  
> -		iir = serial_in(up, UART_IIR);
> +		iir = iir_int_status(up);
>  		if (!(iir & UART_IIR_NO_INT)) {
>  			serial8250_handle_port(up);
>  
> @@ -1732,7 +1762,7 @@ static void serial8250_timeout(unsigned long data)
>  	struct uart_8250_port *up = (struct uart_8250_port *)data;
>  	unsigned int iir;
>  
> -	iir = serial_in(up, UART_IIR);
> +	iir = iir_int_status(up);
>  	if (!(iir & UART_IIR_NO_INT))
>  		serial8250_handle_port(up);
>  	mod_timer(&up->timer, jiffies + poll_timeout(up->port.timeout));
> @@ -1753,7 +1783,7 @@ static void serial8250_backup_timeout(unsigned long data)
>  		serial_out(up, UART_IER, 0);
>  	}
>  
> -	iir = serial_in(up, UART_IIR);
> +	iir = iir_int_status(up);
>  
>  	/*
>  	 * This should be a safe test for anyone who doesn't trust the
> 
>