linux-kernel - Re: ALSA: cs5535audio: fix PRD register save/restore power management race

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Message-ID: <20070830144447.GI5851@cosmic.amd.com>
Date:	Thu, 30 Aug 2007 08:44:47 -0600
From:	"Jordan Crouse" <jordan.crouse@....com>
To:	"Andres Salomon" <dilinger@...ued.net>
cc:	jayakumar.alsa@...il.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, info-linux@...de.amd.com
Subject: Re: ALSA: cs5535audio: fix PRD register save/restore power
 management race

On 29/08/07 23:29 -0400, Andres Salomon wrote:
> 
> In the suspend path, we currently save the PRD registers and then disable DMA.
> This is racy; the sound hardware might update the PRD register as it finishes
> processing some DMA pages between when we've saved the PRD registers and
> when DMA actually gets disabled.  Furthermore, we actively check whether or
> not DMA is enabled before saving PRD registers; there's no reason to do that,
> as the PRD registers should not update when we twiddle the ACC_BM[x]_CMD
> register(s).  Worst case, we save the PRD registers twice; even powering
> down the ACC shouldn't mess with the PRD registers (according to the 5536
> data sheet, section 5.3.7.4, power-down procedure).  This patch reworks
> all that to first disable DMA, and then save PRD registers.
> 
> Signed-off-by: Andres Salomon <dilinger@...ian.org>
Acked-by: Jordan Crouse <jordan.crouse@....com>
> ---
> 
>  sound/pci/cs5535audio/cs5535audio.h     |    1 -
>  sound/pci/cs5535audio/cs5535audio_pcm.c |    2 --
>  sound/pci/cs5535audio/cs5535audio_pm.c  |   14 +++++++-------
>  3 files changed, 7 insertions(+), 10 deletions(-)
> 
> diff --git a/sound/pci/cs5535audio/cs5535audio.h b/sound/pci/cs5535audio/cs5535audio.h
> index 4fd1f31..c7a2044 100644
> --- a/sound/pci/cs5535audio/cs5535audio.h
> +++ b/sound/pci/cs5535audio/cs5535audio.h
> @@ -106,7 +106,6 @@ struct cs5535audio_dma {
>  	struct snd_pcm_substream *substream;
>  	unsigned int buf_addr, buf_bytes;
>  	unsigned int period_bytes, periods;
> -	int suspended;
>  	u32 saved_prd;
>  };
>  
> diff --git a/sound/pci/cs5535audio/cs5535audio_pcm.c b/sound/pci/cs5535audio/cs5535audio_pcm.c
> index e61f972..fe21a1c 100644
> --- a/sound/pci/cs5535audio/cs5535audio_pcm.c
> +++ b/sound/pci/cs5535audio/cs5535audio_pcm.c
> @@ -300,14 +300,12 @@ static int snd_cs5535audio_trigger(struct snd_pcm_substream *substream, int cmd)
>  		break;
>  	case SNDRV_PCM_TRIGGER_RESUME:
>  		dma->ops->enable_dma(cs5535au);
> -		dma->suspended = 0;
>  		break;
>  	case SNDRV_PCM_TRIGGER_STOP:
>  		dma->ops->disable_dma(cs5535au);
>  		break;
>  	case SNDRV_PCM_TRIGGER_SUSPEND:
>  		dma->ops->disable_dma(cs5535au);
> -		dma->suspended = 1;
>  		break;
>  	default:
>  		snd_printk(KERN_ERR "unhandled trigger\n");
> diff --git a/sound/pci/cs5535audio/cs5535audio_pm.c b/sound/pci/cs5535audio/cs5535audio_pm.c
> index 3e4d198..9a4e84a 100644
> --- a/sound/pci/cs5535audio/cs5535audio_pm.c
> +++ b/sound/pci/cs5535audio/cs5535audio_pm.c
> @@ -64,13 +64,13 @@ int snd_cs5535audio_suspend(struct pci_dev *pci, pm_message_t state)
>  	int i;
>  
>  	snd_power_change_state(card, SNDRV_CTL_POWER_D3hot);
> +	snd_pcm_suspend_all(cs5535au->pcm);
> +	snd_ac97_suspend(cs5535au->ac97);
>  	for (i = 0; i < NUM_CS5535AUDIO_DMAS; i++) {
>  		struct cs5535audio_dma *dma = &cs5535au->dmas[i];
> -		if (dma && dma->substream && !dma->suspended) 
> +		if (dma && dma->substream)
>  			dma->saved_prd = dma->ops->read_prd(cs5535au);
>  	}
> -	snd_pcm_suspend_all(cs5535au->pcm);
> -	snd_ac97_suspend(cs5535au->ac97);
>  	/* save important regs, then disable aclink in hw */
>  	snd_cs5535audio_stop_hardware(cs5535au);
>  
> @@ -112,17 +112,17 @@ int snd_cs5535audio_resume(struct pci_dev *pci)
>  	if (!timeout)
>  		snd_printk(KERN_ERR "Failure getting AC Link ready\n");
>  
> -	/* we depend on ac97 to perform the codec power up */
> -	snd_ac97_resume(cs5535au->ac97);
>  	/* set up rate regs, dma. actual initiation is done in trig */
>  	for (i = 0; i < NUM_CS5535AUDIO_DMAS; i++) {
>  		struct cs5535audio_dma *dma = &cs5535au->dmas[i];
> -		if (dma && dma->substream && dma->suspended) {
> +		if (dma && dma->substream) {
>  			dma->substream->ops->prepare(dma->substream);
>  			dma->ops->setup_prd(cs5535au, dma->saved_prd);
>  		}
>  	}
> -		
> +
> +	/* we depend on ac97 to perform the codec power up */
> +	snd_ac97_resume(cs5535au->ac97);
>  	snd_power_change_state(card, SNDRV_CTL_POWER_D0);
>  
>  	return 0;
> 
> 

-- 
Jordan Crouse
Systems Software Development Engineer 
Advanced Micro Devices, Inc.


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