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Date: Tue, 24 Aug 2004 19:27:29 +0200
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From: Takashi Iwai <tiwai@suse.de>
To: karl.vogel@seagha.com
Cc: linux-kernel@vger.kernel.org, Lee Revell <rlrevell@joe-job.com>
Subject: Re: [patch] intel8x0 latency fix
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At Fri, 20 Aug 2004 18:19:12 +0200,
karl.vogel@seagha.com wrote:
> 
> karl.vogel@seagha.com writes:
> 
> > # lspci -s 00:06.0
> > 00:06.0 Multimedia audio controller: nVidia Corporation nForce3 Audio (rev a2)
> >
> >  latency: 50752 us, entries: 267 (267)
> 
> 
> Following patch fixes it for 2 channel devices (like my notebook). Although I'm
> not sure if this is all that useful... if there are workloads other than audio
> work that need low latency, then this might be useful.
> 

In the recent version (linux-sound tree), we can use msleep() (that is
more latency friendely) in that callback.  The following patch was
applied to the current version.


Takashi

--- linux/sound/pci/intel8x0.c	17 Aug 2004 17:09:19 -0000	1.158
+++ linux/sound/pci/intel8x0.c	23 Aug 2004 13:57:52 -0000
@@ -1024,8 +1024,10 @@
 			/* reset to 2ch once to keep the 6 channel data in alignment,
 			 * to start from Front Left always
 			 */
-			iputdword(chip, ICHREG(GLOB_CNT), (cnt & 0xcfffff));
-			mdelay(50); /* grrr... */
+			if (cnt & ICH_PCM_246_MASK) {
+				iputdword(chip, ICHREG(GLOB_CNT), cnt & ~ICH_PCM_246_MASK);
+				msleep(50);
+			}
 		} else if (chip->device_type == DEVICE_INTEL_ICH4) {
 			if (sample_bits > 16)
 				cnt |= ICH_PCM_20BIT;