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Message-Id: <1397282200-10143-1-git-send-email-kys@microsoft.com>
Date: Fri, 11 Apr 2014 22:56:40 -0700
From: "K. Y. Srinivasan" <kys@...rosoft.com>
To: 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, hpa@...or.com, JBeulich@...e.com
Cc: "K. Y. Srinivasan" <kys@...rosoft.com>
Subject: [PATCH V2 1/1] X86: Probe for PIC and set legacy_pic appropriately
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@...ux.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@...rosoft.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
--
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