Re: [PATCH 26/30] loongson: flush irq write operation

[Ralf Baechle <ralf@linux-mips.org>]

On Sat, May 16, 2009 at 06:28:47AM +0800, Wu Zhangjin wrote:

> read back after write, otherwise, there will be many spurious irqs from
> it
> ---
>  arch/mips/kernel/i8259.c               |    5 +++++
>  arch/mips/loongson/common/bonito-irq.c |    4 ++++
>  2 files changed, 9 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/mips/kernel/i8259.c b/arch/mips/kernel/i8259.c
> index 413bd1d..f7c3a2b 100644
> --- a/arch/mips/kernel/i8259.c
> +++ b/arch/mips/kernel/i8259.c
> @@ -175,12 +175,17 @@ handle_real_irq:
>  	if (irq & 8) {
>  		inb(PIC_SLAVE_IMR);	/* DUMMY - (do we need this?) */
>  		outb(cached_slave_mask, PIC_SLAVE_IMR);
> +		inb(PIC_SLAVE_IMR);
>  		outb(0x60+(irq&7), PIC_SLAVE_CMD);/* 'Specific EOI' to slave */
> +		inb(PIC_SLAVE_CMD);
>  		outb(0x60+PIC_CASCADE_IR, PIC_MASTER_CMD); /* 'Specific EOI' to
> master-IRQ2 */
> +		inb(PIC_MASTER_CMD);
>  	} else {
>  		inb(PIC_MASTER_IMR);	/* DUMMY - (do we need this?) */
>  		outb(cached_master_mask, PIC_MASTER_IMR);
> +		inb(PIC_SLAVE_IMR);
>  		outb(0x60+irq, PIC_MASTER_CMD);	/* 'Specific EOI to master */
> +		inb(PIC_MASTER_CMD);
>  	}
>  	smtc_im_ack_irq(irq);
>  	spin_unlock_irqrestore(&i8259A_lock, flags);

The semantic of inX() / outX() is defined by the x86 architecture which
forbids posting I/O port writes.  In short I think this one is papering
over a bug in the outX() implementation.

I'm ok with the bonito part of this patch.

  Ralf