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

[yanh <yanh@lemote.com>]

在 2009-05-19二的 17:01 +0100，Ralf Baechle写道：
> 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

Thanks for your reply.
As my test, if there is no the read, there will be many spurious irqs. 
> 
> 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?
I have test this patch just now. It works well on yeeloong. 
I have one question what's the difference between the two patch? 
> 
>   Ralf