[PATCH V2 1/1] X86: Probe for PIC and set legacy_pic appropriately

[PATCH V2 1/1] X86: Probe for PIC and set legacy_pic appropriately

[K. Y. Srinivasan]

Probe for the existance of legacy PIC, if one does not exist, use the
null_legacy_pic.

This patch implements the proposal put forth by H. Peter Anvin <hpa@linux.intel.com>.

In  version V1 of the patch, I had cleaned up the code based on comments from
Peter.

In this version of the patch, I have addressed additional comments from Peter.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
---
 arch/x86/kernel/cpu/mshyperv.c |    2 --
 arch/x86/kernel/i8259.c        |   19 +++++++++++++++++++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 47359f7..9ca9587 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -133,8 +133,6 @@ static void __init ms_hyperv_init_platform(void)
 		printk(KERN_INFO "HyperV: LAPIC Timer Frequency: %#x\n",
 				lapic_timer_frequency);
 
-		printk(KERN_INFO "HyperV: Using null_legacy_pic\n");
-		legacy_pic = &null_legacy_pic;
 	}
 #endif
 
diff --git a/arch/x86/kernel/i8259.c b/arch/x86/kernel/i8259.c
index 2e977b5..7f7bd02 100644
--- a/arch/x86/kernel/i8259.c
+++ b/arch/x86/kernel/i8259.c
@@ -299,11 +299,30 @@ static void unmask_8259A(void)
 static void init_8259A(int auto_eoi)
 {
 	unsigned long flags;
+	unsigned char probe_val = ~(1 << PIC_CASCADE_IR);
+	unsigned char new_val;
 
 	i8259A_auto_eoi = auto_eoi;
 
 	raw_spin_lock_irqsave(&i8259A_lock, flags);
 
+	/*
+	 * 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(0xff, PIC_SLAVE_IMR);	/* mask all of 8259A-2 */
+	outb(probe_val, PIC_MASTER_IMR);
+	new_val = inb(PIC_MASTER_IMR);
+	if (probe_val != new_val) {
+		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 */
 
-- 
1.7.4.1

Re: [PATCH V2 1/1] X86: Probe for PIC and set legacy_pic appropriately

[Jan Beulich]

>>> On 12.04.14 at 07:56, <kys@microsoft.com> wrote:
> --- a/arch/x86/kernel/i8259.c
> +++ b/arch/x86/kernel/i8259.c
> @@ -299,11 +299,30 @@ static void unmask_8259A(void)
>  static void init_8259A(int auto_eoi)
>  {
>  	unsigned long flags;
> +	unsigned char probe_val = ~(1 << PIC_CASCADE_IR);
> +	unsigned char new_val;
>  
>  	i8259A_auto_eoi = auto_eoi;
>  
>  	raw_spin_lock_irqsave(&i8259A_lock, flags);
>  
> +	/*
> +	 * 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(0xff, PIC_SLAVE_IMR);	/* mask all of 8259A-2 */
> +	outb(probe_val, PIC_MASTER_IMR);
> +	new_val = inb(PIC_MASTER_IMR);
> +	if (probe_val != new_val) {
> +		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 */

And I guess you should delete this last line now that this is already
being done slightly earlier - having it done twice is possibly going to
confuse future readers (in that they might ask themselves or others
whether this really needs to be done twice).

Jan

Re: [PATCH V2 1/1] X86: Probe for PIC and set legacy_pic appropriately

[Olaf Hering]

On Fri, Apr 11, K. Y. Srinivasan wrote:

> Probe for the existance of legacy PIC, if one does not exist, use the
> null_legacy_pic.

> Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>

Tested-by: Olaf Hering <olaf@aepfle.de>

Fixes the crash on Gen1 VMs for me, which was introduced by
"x86/platform/hyperv: When on Hyper-v use NULL legacy PIC".

Olaf

RE: [PATCH V2 1/1] X86: Probe for PIC and set legacy_pic appropriately

[KY Srinivasan]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@suse.com]
> Sent: Monday, April 14, 2014 1:15 AM
> To: KY Srinivasan
> Cc: olaf@aepfle.de; apw@canonical.com; x86@kernel.org;
> tglx@linutronix.de; devel@linuxdriverproject.org;
> gregkh@linuxfoundation.org; jasowang@redhat.com; linux-
> kernel@vger.kernel.org; hpa@zytor.com
> Subject: Re: [PATCH V2 1/1] X86: Probe for PIC and set legacy_pic
> appropriately
> 
> >>> On 12.04.14 at 07:56, <kys@microsoft.com> wrote:
> > --- a/arch/x86/kernel/i8259.c
> > +++ b/arch/x86/kernel/i8259.c
> > @@ -299,11 +299,30 @@ static void unmask_8259A(void)  static void
> > init_8259A(int auto_eoi)  {
> >  	unsigned long flags;
> > +	unsigned char probe_val = ~(1 << PIC_CASCADE_IR);
> > +	unsigned char new_val;
> >
> >  	i8259A_auto_eoi = auto_eoi;
> >
> >  	raw_spin_lock_irqsave(&i8259A_lock, flags);
> >
> > +	/*
> > +	 * 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(0xff, PIC_SLAVE_IMR);	/* mask all of 8259A-2 */
> > +	outb(probe_val, PIC_MASTER_IMR);
> > +	new_val = inb(PIC_MASTER_IMR);
> > +	if (probe_val != new_val) {
> > +		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 */
> 
> And I guess you should delete this last line now that this is already being
> done slightly earlier - having it done twice is possibly going to confuse future
> readers (in that they might ask themselves or others whether this really
> needs to be done twice).

Good point! I will fix this and resend.

K. Y
> 
> Jan