[alsa-devel] [PATCH] ALSA: ctxfi - Work around emu20k1 glitch to prevent buffered sound data loss

[Takashi Iwai]

At Thu, 9 Jan 2014 11:36:31 -0800,
Sarah Bessmer wrote:
> 
> Occasionally, on playback stream ringbuffer wraparound, the EMU20K1
> hardware will momentarily return 0 instead of the proper current(loop)
> address. This patch handles that case, fixing the problem of playback
> position corruption and subsequent loss of buffered sound data, that
> occurs with some common buffering layout patterns(e.g. multiple
> simultaneous output streams with differently-sized or
> non-power-of-2-sized buffers).
> 
> An alternate means of fixing the problem would be to read the ca
> register continuously, until two sequential reads return the same
> value; however, that would be a more invasive change, has performance
> implications, and isn't necessary unless there are also issues with the
> value not being updated atomically in regards to individual bits or
> something similar(which I have not encountered through light testing).
> 
> I have no EMU20K2 hardware to confirm if the issue is present there,
> but even if it's not, this change shouldn't break anything that's not
> already broken.
> 
> Signed-off-by: Sarah Bessmer <aotos at fastmail.fm>
> Cc: Takashi Iwai <tiwai at suse.de>

Thanks, applied with a space fix.


Takashi

> ---
> --- linux-3.10.25/sound/pci/ctxfi/ctatc.c.orig	2014-01-09 10:12:00.000000000 -0800
> +++ linux-3.10.25/sound/pci/ctxfi/ctatc.c	2014-01-09 10:32:42.000000000 -0800
> @@ -433,10 +433,15 @@ atc_pcm_playback_position(struct ct_atc
>  
>  	if (!src)
>  		return 0;
>  	position = src->ops->get_ca(src);
>  
> +	if(position < apcm->vm_block->addr) {
> +		snd_printdd("ctxfi: bad ca - ca=0x%08x, vba=0x%08x, vbs=0x%08x\n", position, apcm->vm_block->addr, apcm->vm_block->size);
> +		position = apcm->vm_block->addr;
> +	}
> +
>  	size = apcm->vm_block->size;
>  	max_cisz = src->multi * src->rsc.msr;
>  	max_cisz = 128 * (max_cisz < 8 ? max_cisz : 8);
>  
>  	return (position + size - max_cisz - apcm->vm_block->addr) % size;
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