Patchwork [U-Boot,v2,1/5] input: Use finer grain udelays while waitng for the i8042 keyboard buffer to empty

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Submitter Simon Glass
Date Oct. 13, 2012, 12:02 a.m.
Message ID <1350086525-22030-1-git-send-email-sjg@chromium.org>
Download mbox | patch
Permalink /patch/191249/
State Accepted, archived
Delegated to: Tom Rini
Headers show

Comments

Simon Glass - Oct. 13, 2012, 12:02 a.m.
From: Gabe Black <gabeblack@chromium.org>

On x86, the i8042 keyboard controller driver frequently waits for the keyboard
input buffer to be empty to make sure the controller has had a chance to
process the data it was given. The way the delay loop was structured, if the
controller hadn't cleared the corresponding status bit immediately, it would
wait 1ms before checking again. If the keyboard responded quickly but not
instantly, the driver would still wait a full 1ms when perhaps 1us would have
been sufficient. Because udelay is a busy wait anyway, this change decreases
the delay between checks to 1us.

Also, this change gets rid of a hardcoded 250ms delay.

On Stumpy, this saves 100-150ms during boot.

Signed-off-by: Gabe Black <gabeblack@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>
---
Changes in v2:
- Add constants for i8042 status registers

 drivers/input/i8042.c |    9 +++------
 include/i8042.h       |    6 ++++++
 2 files changed, 9 insertions(+), 6 deletions(-)

Patch

diff --git a/drivers/input/i8042.c b/drivers/input/i8042.c
index c3bc536..6839c6b 100644
--- a/drivers/input/i8042.c
+++ b/drivers/input/i8042.c
@@ -607,11 +607,10 @@  static void kbd_led_set(void)
 
 static int kbd_input_empty(void)
 {
-	int kbdTimeout = KBD_TIMEOUT;
+	int kbdTimeout = KBD_TIMEOUT * 1000;
 
-	/* wait for input buf empty */
-	while ((in8(I8042_STATUS_REG) & 0x02) && kbdTimeout--)
-		udelay(1000);
+	while ((in8(I8042_STATUS_REG) & I8042_STATUS_IN_DATA) && kbdTimeout--)
+		udelay(1);
 
 	return kbdTimeout != -1;
 }
@@ -625,8 +624,6 @@  static int kbd_reset(void)
 
 	out8(I8042_DATA_REG, 0xff);
 
-	udelay(250000);
-
 	if (kbd_input_empty() == 0)
 		return -1;
 
diff --git a/include/i8042.h b/include/i8042.h
index 1395289..aeb3f09 100644
--- a/include/i8042.h
+++ b/include/i8042.h
@@ -39,6 +39,12 @@ 
 #define I8042_STATUS_REG    (CONFIG_SYS_ISA_IO + 0x0064)    /* keyboard status read */
 #define I8042_COMMAND_REG   (CONFIG_SYS_ISA_IO + 0x0064)    /* keyboard ctrl write */
 
+enum {
+	/* Output register (I8042_DATA_REG) has data for system */
+	I8042_STATUS_OUT_DATA	= 1 << 0,
+	I8042_STATUS_IN_DATA	= 1 << 1,
+};
+
 #define KBD_US              0        /* default US layout */
 #define KBD_GER             1        /* german layout */