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Subject[PATCH V3 1/1] X86: Probe for PIC and set legacy_pic appropriately
Date
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 version V2 of the patch, I have addressed additional comments from Peter.
In this version of the patch, I have addressed Jan's comments (JBeulich@suse.com).

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
---
arch/x86/kernel/cpu/mshyperv.c | 2 --
arch/x86/kernel/i8259.c | 20 +++++++++++++++++++-
2 files changed, 19 insertions(+), 3 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..d5447f1 100644
--- a/arch/x86/kernel/i8259.c
+++ b/arch/x86/kernel/i8259.c
@@ -299,13 +299,31 @@ 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);

- outb(0xff, PIC_MASTER_IMR); /* mask all of 8259A-1 */
+ /*
+ * 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_pic - this has to work on a wide range of PC hardware.
--
1.7.4.1


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