Re: [PATCH] ALSA: loongson: Fix invalid position error in ls_pcm_pointer

[lijun]

When the addr is abnormal, such as when the DMA controller is abnormal,
I think x=0 should not be a point, but a range, which includes the addr
address being less than runtime ->dma1-adr, and the addr exceeding
the DMA address range.

在 2026/5/29 17:01, Takashi Iwai 写道:
> On Fri, 29 May 2026 04:48:30 +0200,
> Li Jun wrote:
> > The "invalid position" error occurred when the DMA position descriptor
> > returned an invalid address value (e.g., pos = -1048838144). This happened
> > because the `bytes_to_frames()` function returns a signed value, but when
> > `addr < runtime->dma_addr`, the subtraction produces a negative result that
> > gets interpreted as a large unsigned integer in comparisons.
> >
> > [   32.834431][ 2]  soc-audio soc-audio: invalid position: , pos = -1048838144
> > [   32.845019][ 2]  soc-audio soc-audio: invalid position: , pos = -1048838144
> > [   32.855588][ 2]  soc-audio soc-audio: invalid position: , pos = -1048838144
> > [   32.866145][ 2]  soc-audio soc-audio: invalid position: , pos = -1048838144
> > [   32.995394][ 2]  soc-audio soc-audio: invalid position: , pos = -1048838144
> > [   33.006025][ 2]  soc-audio soc-audio: invalid position: , pos = -1048838144
> > [   33.016748][ 2]  soc-audio soc-audio: invalid position: , pos = -1048838144
> >
> > Signed-off-by: Li Jun <lijun01@xxxxxxxxxx>
> Since it's a change for ASoC, use "ASoC" prefix for the subject line.
>
> About the code change: how does this negative position come?  Is it an
> utterly bogus value to be ignored, or is it a position overlap or
> such?  Your change seems just ignoring and returning 0, and if it's a
> spontaneous bogus value, it may lead to an unexpected jump of the PCM
> position, too, for example.
>
>
> thanks,
>
> Takashi
>
> > ---
> >   sound/soc/loongson/loongson_dma.c | 10 ++++++++--
> >   1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/sound/soc/loongson/loongson_dma.c b/sound/soc/loongson/loongson_dma.c
> > index a149b643175c..f0a7065ddae7 100644
> > --- a/sound/soc/loongson/loongson_dma.c
> > +++ b/sound/soc/loongson/loongson_dma.c
> > @@ -207,9 +207,15 @@ loongson_pcm_pointer(struct snd_soc_component *component,
> >   	desc = dma_desc_save(prtd);
> >   	addr = ((u64)desc->saddr_hi << 32) | desc->saddr;
> >   
> > -	x = bytes_to_frames(runtime, addr - runtime->dma_addr);
> > -	if (x == runtime->buffer_size)
> > +	if (addr < runtime->dma_addr ||
> > +	    addr >= runtime->dma_addr + runtime->dma_bytes) {
> >   		x = 0;
> > +	} else {
> > +		x = bytes_to_frames(runtime, addr - runtime->dma_addr);
> > +		if (x >= runtime->buffer_size)
> > +			x = 0;
> > +	}
> > +
> >   	return x;
> >   }
> >   
> > --
> > 2.25.1