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

To: Wu Zhangjin <wuzhangjin@gmail.com>
Subject: Re: [PATCH 26/30] loongson: flush irq write operation
From: Ralf Baechle <ralf@linux-mips.org>
Date: Mon, 18 May 2009 17:36:03 +0100
Cc: linux-mips@linux-mips.org, Arnaud Patard <apatard@mandriva.com>, loongson-dev@googlegroups.com, zhangfx@lemote.com, yanh@lemote.com, Philippe Vachon <philippe@cowpig.ca>, Zhang Le <r0bertz@gentoo.org>, Erwan Lerale <erwan@thiscow.com>
In-reply-to: <1242426527.10164.174.camel@falcon>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <1242426527.10164.174.camel@falcon>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.5.18 (2008-05-17)
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

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