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

To: yanh <yanh@lemote.com>
Subject: Re: [PATCH 26/30] loongson: flush irq write operation
From: Ralf Baechle <ralf@linux-mips.org>
Date: Tue, 19 May 2009 17:01:17 +0100
Cc: Wu Zhangjin <wuzhangjin@gmail.com>, linux-mips@linux-mips.org, Arnaud Patard <apatard@mandriva.com>, loongson-dev@googlegroups.com, zhangfx@lemote.com, Philippe Vachon <philippe@cowpig.ca>, Zhang Le <r0bertz@gentoo.org>, Erwan Lerale <erwan@thiscow.com>
In-reply-to: <1242700637.4382.21.camel@localhost.localdomain>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <1242426527.10164.174.camel@falcon> <20090518163603.GA22779@linux-mips.org> <1242700637.4382.21.camel@localhost.localdomain>
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User-agent: Mutt/1.5.18 (2008-05-17)
On Tue, May 19, 2009 at 10:37:17AM +0800, yanh wrote:

> > 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.
> Yes, the outX should do a delayed write, however it does not. 
> So our solution is making a read to flush the write.

Do you actually need all the inb() you added to get things to work or is

diff --git a/arch/mips/kernel/i8259.c b/arch/mips/kernel/i8259.c
index 01c0885..42d75d7 100644
--- a/arch/mips/kernel/i8259.c
+++ b/arch/mips/kernel/i8259.c
@@ -177,10 +177,12 @@ handle_real_irq:
                outb(cached_slave_mask, PIC_SLAVE_IMR);
                outb(0x60+(irq&7), PIC_SLAVE_CMD);/* 'Specific EOI' to slave */
                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);
                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);

sufficient to solve the problem?

  Ralf

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