[alsa-devel] [PATCH] hda - remove unnecessary msleep on power state transitions

[Wu Fengguang]

From: "Zhang, Rui" <rui.zhang at intel.com>

This will save ~15ms boot time.

The first 10ms sleep was introduced in commit d2595d86e5 for (buggy)
Cxt codecs, so better to limit the sleep to the problem hardware.

For the second 10ms sleep, the HDA spec says:

Power State[1:0]:
00: Node Power state (D0) is fully on.
01: Node Power state (D1) allows for (does not require) the lowest possible power consuming state from which it
can return to the "fully on" state (D0) within 10 ms, excepting analog pass through circuits (e.g., CD analog
playback) which must remain fully on.
10: Node Power state (D2) allows for (does not require) the lowest possible power consuming state from which it
can return to the "fully on" state (D0) within 10 ms. For modems, this is the "wake on ring" power state.
11: Node Power state (D3) allows for (does not require) lowest possible power consuming state under software
control. Note that any low power state set by software must retain sufficient operational capability to properly
respond to subsequent software Power State command.

So 10ms is actually the max wait time. It should be safe to
remove/reduce it and rely on the loop of 1ms-sleeps.

CC: Marc Boucher <marc at linuxant.com>
CC: Arjan van de Ven <arjan at linux.intel.com>
Signed-off-by: Zhang Rui <rui.zhang at intel.com>
Signed-off-by: Wu Fengguang <fengguang.wu at intel.com>
---
 sound/pci/hda/hda_codec.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- sound-2.6.orig/sound/pci/hda/hda_codec.c	2010-01-13 09:41:49.000000000 +0800
+++ sound-2.6/sound/pci/hda/hda_codec.c	2010-02-24 09:34:14.000000000 +0800
@@ -2767,7 +2767,8 @@ static void hda_set_power_state(struct h
 	snd_hda_codec_read(codec, fg, 0, AC_VERB_SET_POWER_STATE,
 			    power_state);
 	/* partial workaround for "azx_get_response timeout" */
-	if (power_state == AC_PWRST_D0)
+	if (power_state == AC_PWRST_D0 &&
+	    codec->vendor_id & 0xffff0000 == 0x14f10000)
 		msleep(10);
 
 	nid = codec->start_nid;
@@ -2801,7 +2802,6 @@ static void hda_set_power_state(struct h
 	if (power_state == AC_PWRST_D0) {
 		unsigned long end_time;
 		int state;
-		msleep(10);
 		/* wait until the codec reachs to D0 */
 		end_time = jiffies + msecs_to_jiffies(500);
 		do {