linux-kernel - Re: [PATCH -queue v0 4/6] [loongson] add basic fuloong2f support

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Date:	Fri, 6 Nov 2009 09:30:42 +0100
From:	Ralf Baechle <ralf@...ux-mips.org>
To:	Wu Zhangjin <wuzhangjin@...il.com>
Cc:	linux-mips@...ux-mips.org, LKML <linux-kernel@...r.kernel.org>,
	huhb@...ote.com, yanh@...ote.com, Zhang Le <r0bertz@...too.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nicholas Mc Guire <der.herr@...r.at>, zhangfx@...ote.com,
	liujl@...ote.com
Subject: Re: [PATCH -queue v0 4/6] [loongson] add basic fuloong2f support

On Fri, Nov 06, 2009 at 01:39:44PM +0800, Wu Zhangjin wrote:

> > > +	if ((LOONGSON_INTISR & LOONGSON_INTEN) & LOONGSON_INT_BIT_INT0) {
> > > +		imr = inb(0x21) | (inb(0xa1) << 8);
> > > +		isr = inb(0x20) | (inb(0xa0) << 8);
> > > +		isr &= ~0x4;	/* irq2 for cascade */
> > > +		isr &= ~imr;
> > > +		irq = ffs(isr) - 1;
> > > +	}
> > 
> > Any reason why you're not using i8259_irq() from <asm/i8259.h> here?
> > That function not only gets the locking right, it also minimizes the number
> > of accesses to the i8259 - which even on modern silicon can be stuningly
> > slow.

> Just asked Yanhua, He told me there is a bug in cs5536, if using the
> i8259_irq() directly, we can not get the irq. and just tried it, the
> kernel hang on booting.

Wonderful.  Even 30 years after it was built there are still new i8259
bugs :-)

This is probably worth a comment in the code.

  Ralf
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