[alsa-devel] customized IOCTL in pcm platform driver.

[Takashi Iwai]

At Tue, 9 Oct 2012 00:30:40 -0700 (PDT),
gsantosh at codeaurora.org wrote:
> 
> > At Mon, 8 Oct 2012 23:44:40 -0700 (PDT),
> > gsantosh at codeaurora.org wrote:
> >>
> >> > At Mon, 8 Oct 2012 23:30:09 -0700 (PDT),
> >> > gsantosh at codeaurora.org wrote:
> >> >>
> >> >> Hi All,
> >> >>
> >> >> will ALSA framework provide any customized IOCTL functionality in PCM
> >> >> platform driver.
> >> >
> >> > No.
> >> >
> >> >> in my  system there is a requirement to get some information from DSP
> >> to
> >> >> user space and I am thinking to add IOCTL's, is there any method to
> >> >> accommodate or how we can address this issue?
> >> >
> >> > You can use hwdep device for any extra methods.
> >>
> >> We need to tie this ioctl with the on going DSP session which will be
> >> difficult When used with hwdep interface.
> >
> > Hm, how can it be difficult?  More specific description is needed to
> > answer more.
> 
> to communicate with DSP we open up a session and populate that information
> in the substream, for this use case during the playback session user space
> has to talk to DSP to get some information like time stamp also the time
> stamp statistics, to talk to DSP I need to get hold of the proper
> substream so that the communication with particular session is possible.
> 
> I see adding one IOCTL in the platform driver will solve my issue, but not
> finding any way to integrate this in the current framework,
> 
> if we use the hwdep, not sure how can I get hold of the substream handle
> so I can talk to particular session in DSP.

A PCM substream can be identified simply by a PCM device number and
a PCM substream index.  You can make ioctl to pass these information.


Takashi