[PATCH] x86: use explicit timing delay for pit accesses in kernel and pcspkr driver

[David P. Reed]

x86: use explicit timing delay for pit accesses in kernel and pcspkr driver

pit accesses in i8253.c and pcspkr driver use outb_p for timing.
Fix them to use explicit timing delay for access to PIT,
rather than inb_p/outb_p calls, which use insufficiently explicit
delays (defaulting to port 80 writes) that can cause freeze problems
on some machines, such as Quanta moterboard  machines using ENE EC's.

Since the pcspkr driver accesses PIT registers directly, it should also
use outb_pit, which is inlined, so does not need bo exported.
Explicit timing delay is only needed in pcspkr for accesses to the 8253 PIT.
Fix pcspkr driver to use the new outb_pic call properly, use
named PIC port values rather than hex constants, and drop its use of
inb_p and outb_p in accessing port 61h where it has never been needed.

Signed-off-by: David P. Reed <dpreed@xxxxxxxx>

Index: linux-2.6/drivers/input/misc/pcspkr.c
===================================================================
--- linux-2.6.orig/drivers/input/misc/pcspkr.c
+++ linux-2.6/drivers/input/misc/pcspkr.c
@@ -36,6 +36,7 @@ static int pcspkr_event(struct input_dev
 {
 	unsigned int count = 0;
 	unsigned long flags;
+	unsigned char port61;
 
 	if (type != EV_SND)
 		return -1;
@@ -51,17 +52,18 @@ static int pcspkr_event(struct input_dev
 
 	spin_lock_irqsave(&i8253_lock, flags);
 
+	port61 = inb(0x61);
 	if (count) {
 		/* enable counter 2 */
-		outb_p(inb_p(0x61) | 3, 0x61);
+		outb(port61 | 3, 0x61);
 		/* set command for counter 2, 2 byte write */
-		outb_p(0xB6, 0x43);
+		outb_pit(0xB6, PIT_MODE);
 		/* select desired HZ */
-		outb_p(count & 0xff, 0x42);
-		outb((count >> 8) & 0xff, 0x42);
+		outb_pit(count & 0xff, PIT_CH2);
+		outb((count >> 8) & 0xff, PIT_CH2);
 	} else {
 		/* disable counter 2 */
-		outb(inb_p(0x61) & 0xFC, 0x61);
+		outb(port61 & 0xFC, 0x61);
 	}
 
 	spin_unlock_irqrestore(&i8253_lock, flags);
Index: linux-2.6/include/asm-x86/i8253.h
===================================================================
--- linux-2.6.orig/include/asm-x86/i8253.h
+++ linux-2.6/include/asm-x86/i8253.h
@@ -12,7 +12,25 @@ extern struct clock_event_device *global
 
 extern void setup_pit_timer(void);
 
-#define inb_pit		inb_p
-#define outb_pit	outb_p
+/* accesses to PIT registers need careful delays on some platforms. Define
+   them here in a common place */
+static inline unsigned char inb_pit(unsigned int port)
+{
+	/* delay for some accesses to PIT on motherboard or in chipset must be
+	   at least one microsecond, but be safe here. */
+	unsigned char value = inb(port);
+	udelay(2);
+	return value;
+}
+
+static inline void outb_pit(unsigned char value, unsigned int port)
+{
+	/* delay for some accesses to PIT on motherboard or in chipset must be
+	   at least one microsecond, but be safe here. */
+	outb(value, port);
+	udelay(2);
+}
+
+
 
 #endif	/* __ASM_I8253_H__ */
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/