[alsa-devel] [PATCH 1/1] ALSA: intel8x0: Improve comments for VM optimization

[Takashi Iwai]

At Mon, 7 Nov 2011 20:33:25 +0400,
Denis V. Lunev wrote:
> 
> The recently merged 228cf79376f1 looks a bit hackish while it is not.
> The change was quite simple. In a virtualized environment the
> patch unhacks old kludge introduced for old broken AC97 hardware.
> 
> This patch adds proper comment to "unkludge" code.
> 
> Signed-off-by: Denis V. Lunev <den at openvz.org>
> Signed-off-by: Konstantin Ozerkov <kozerkov at parallels.com>

Applied now.  Thanks.


Takashi

> ---
>  sound/pci/intel8x0.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
> 
> diff --git a/sound/pci/intel8x0.c b/sound/pci/intel8x0.c
> index 29e3125..c3b9bd0 100644
> --- a/sound/pci/intel8x0.c
> +++ b/sound/pci/intel8x0.c
> @@ -1077,6 +1077,13 @@ static snd_pcm_uframes_t snd_intel8x0_pcm_pointer(struct snd_pcm_substream *subs
>  		}
>  		if (civ != igetbyte(chip, ichdev->reg_offset + ICH_REG_OFF_CIV))
>  			continue;
> +
> +		/* IO read operation is very expensive inside virtual machine
> +		 * as it is emulated. The probability that subsequent PICB read
> +		 * will return different result is high enough to loop till
> +		 * timeout here.
> +		 * Same CIV is strict enough condition to be sure that PICB
> +		 * is valid inside VM on emulated card. */
>  		if (chip->inside_vm)
>  			break;
>  		if (ptr1 == igetword(chip, ichdev->reg_offset + ichdev->roff_picb))
> -- 
> 1.7.4.4
>