linux-kernel - RE: [PATCH V1 1/1] X86: Probe for PIC and set legacy

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Date:	Sat, 12 Apr 2014 02:46:23 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	"H. Peter Anvin" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"JBeulich@...e.com" <JBeulich@...e.com>
Subject: RE: [PATCH V1 1/1] X86: Probe for PIC and set legacy_pic
 appropriately



> -----Original Message-----
> From: H. Peter Anvin [mailto:hpa@...or.com]
> Sent: Friday, April 11, 2014 4:59 PM
> To: KY Srinivasan; x86@...nel.org; gregkh@...uxfoundation.org; linux-
> kernel@...r.kernel.org; devel@...uxdriverproject.org; olaf@...fle.de;
> apw@...onical.com; jasowang@...hat.com; tglx@...utronix.de;
> JBeulich@...e.com
> Subject: Re: [PATCH V1 1/1] X86: Probe for PIC and set legacy_pic
> appropriately
> 
> On 04/11/2014 05:50 PM, K. Y. Srinivasan wrote:
> >
> > +	/*
> > +	 * Check to see if we have a PIC.
> > +	 * Mask all except the cascade and read
> > +	 * back the value we just wrote. If we don't
> > +	 * have a PIC, we will read 0xff as opposed to the
> > +	 * value we wrote.
> > +	 */
> > +	outb(probe_val, PIC_MASTER_IMR);
> > +	probe_val = inb(PIC_MASTER_IMR);
> > +	if (probe_val == 0xff) {
> > +		printk(KERN_INFO "Using NULL legacy PIC\n");
> > +		legacy_pic = &null_legacy_pic;
> > +		raw_spin_unlock_irqrestore(&i8259A_lock, flags);
> > +		return;
> > +	}
> > +
> >  	outb(0xff, PIC_MASTER_IMR);	/* mask all of 8259A-1 */
> >  	outb(0xff, PIC_SLAVE_IMR);	/* mask all of 8259A-2 */
> >
> 
> Again, I would do at least the slave masking above the probe.
> 
> Also, I would compare to make sure we get the probe_val back and compare
> with != instead of comparing with ==.

Will do.

Thanks,

K. Y