[alsa-devel] [PATCH] alsa-lib: update linked hw_ptr and appl_ptr

[Takashi Iwai]

On Thu, 08 Dec 2016 11:56:12 +0100,
Sutar, Mounesh wrote:
> 
> Hi Takashi,
> This is the update I got from Andreas:
> 
> "This is not a generic problem, but can be observed in plugins which use manual linking method.
> The plugins such as PLUG, FILE, METER, MULTI and HOOK use manual linkage.
> PLUG is the 'bad guy' which might change the linking in hw_param operation.
> METER and MULTI might need to be fixed as well.
> HOOKS does not use transfer/processing of frames, so seems harmless (but not 100% sure- linkage should be updated for completeness) 
> 
> The current fix is provided for FILE plugin ONLY"

OK, now I applied the patch as is.  The change callback handling would
be good if we really have, but let's cover the bug quickly for now.


thanks,

Takashi

> 
> Regards,
> Mounesh
> 
> 
> -----Original Message-----
> From: Takashi Iwai [mailto:tiwai at suse.de] 
> Sent: 29 November 2016 00:46
> To: sutar.mounesh at gmail.com
> Cc: alsa-devel at alsa-project.org; Sutar, Mounesh <Mounesh_Sutar at mentor.com>; Andreas Pape <apape at de.adit-jv.com>
> Subject: Re: [PATCH] alsa-lib: update linked hw_ptr and appl_ptr
> 
> On Fri, 25 Nov 2016 11:25:05 +0100,
> sutar.mounesh at gmail.com wrote:
> > 
> > From: Andreas Pape <apape at de.adit-jv.com>
> > 
> > Plugin file provides no private hw_ptr and appl_ptr but instead links them to the slave pcm.
> > If the slave pcm itself changes its hw_ptr or app_prt this needs to be done in file plugin, too.
> > Plugin 'plug' is such a candidate changing the hw_ptr and app_ptr in hw_params call dependent on the automatically inserted plugins.
> > ALSA unfortunately has no support for automatically updating chained pointers.
> > A notification on pointer change seems to be prepared inside the 
> > snd_pcm_set_ptr() routine via
> > rbptr->changed(), but it is not (yet) implemented so that we need to care for it manually.
> > 
> > Signed-off-by: Andreas Pape <apape at de.adit-jv.com>
> 
> Judging from the description, isn't it a generic problem, not specific to file plugin?
> 
> 
> thanks,
> 
> Takashi
> 
> > ---
> >  src/pcm/pcm_file.c |    8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/src/pcm/pcm_file.c b/src/pcm/pcm_file.c index 
> > fec76eb..1e3d35b 100644
> > --- a/src/pcm/pcm_file.c
> > +++ b/src/pcm/pcm_file.c
> > @@ -634,6 +634,14 @@ static int snd_pcm_file_hw_params(snd_pcm_t *pcm, snd_pcm_hw_params_t * params)
> >  			return err;
> >  		}
> >  	}
> > +
> > +	/* pointer may have changed - e.g if plug is used. */
> > +	snd_pcm_unlink_hw_ptr(pcm, file->gen.slave);
> > +	snd_pcm_unlink_appl_ptr(pcm, file->gen.slave);
> > +
> > +	snd_pcm_link_hw_ptr(pcm, file->gen.slave);
> > +	snd_pcm_link_appl_ptr(pcm, file->gen.slave);
> > +
> >  	return 0;
> >  }
> >  
> > --
> > 1.7.9.5
> > 
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