x86, pic: Introduce legacy_pic abstraction

This patch makes i8259A like legacy programmable interrupt controller
code into a driver so that legacy pic functions can be selected at
runtime based on platform information, such as HW subarchitecure ID.
Default structure of legacy_pic maintains the current code path for
x86pc.

Signed-off-by: Jacob Pan <jacob.jun.pan@intel.com>
LKML-Reference: <43F901BD926A4E43B106BF17856F07559FB80D03@orsmsx508.amr.corp.intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/include/asm/i8259.h

@@ -57,6 +57,19 @@ static inline void outb_pic(unsigned char value, unsigned int port)
 
 extern struct irq_chip i8259A_chip;
 
+struct legacy_pic {
+	int nr_legacy_irqs;
+	struct irq_chip *chip;
+	void (*mask_all)(void);
+	void (*restore_mask)(void);
+	void (*init)(int auto_eoi);
+	int (*irq_pending)(unsigned int irq);
+	void (*make_irq)(unsigned int irq);
+};
+
+extern struct legacy_pic *legacy_pic;
+extern struct legacy_pic null_legacy_pic;
+
 extern void mask_8259A(void);
 extern void unmask_8259A(void);
 

arch/x86/kernel/i8259.c

@@ -358,3 +358,46 @@ void init_8259A(int auto_eoi)
 
 	spin_unlock_irqrestore(&i8259A_lock, flags);
 }
+/*
+ * make i8259 a driver so that we can select pic functions at run time. the goal
+ * is to make x86 binary compatible among pc compatible and non-pc compatible
+ * platforms, such as x86 MID.
+ */
+
+static void __init legacy_pic_noop(void) { };
+static void __init legacy_pic_uint_noop(unsigned int unused) { };
+static void __init legacy_pic_int_noop(int unused) { };
+
+static struct irq_chip dummy_pic_chip  = {
+	.name = "dummy pic",
+	.mask = legacy_pic_uint_noop,
+	.unmask = legacy_pic_uint_noop,
+	.disable = legacy_pic_uint_noop,
+	.mask_ack = legacy_pic_uint_noop,
+};
+static int legacy_pic_irq_pending_noop(unsigned int irq)
+{
+	return 0;
+}
+
+struct legacy_pic null_legacy_pic = {
+	.nr_legacy_irqs = 0,
+	.chip = &dummy_pic_chip,
+	.mask_all = legacy_pic_noop,
+	.restore_mask = legacy_pic_noop,
+	.init = legacy_pic_int_noop,
+	.irq_pending = legacy_pic_irq_pending_noop,
+	.make_irq = legacy_pic_uint_noop,
+};
+
+struct legacy_pic default_legacy_pic = {
+	.nr_legacy_irqs = NR_IRQS_LEGACY,
+	.chip  = &i8259A_chip,
+	.mask_all  = mask_8259A,
+	.restore_mask = unmask_8259A,
+	.init = init_8259A,
+	.irq_pending = i8259A_irq_pending,
+	.make_irq = make_8259A_irq,
+};
+
+struct legacy_pic *legacy_pic = &default_legacy_pic;