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

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Date:	Fri, 11 Apr 2014 16:59:23 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"K. Y. Srinivasan" <kys@...rosoft.com>, 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 ==.

	-hpa


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