Re: [PATCH]snd-usb-usx2y 0.8.7: Use macro usb_maxpacket() for portability

[Takashi Iwai <tiwai@suse.de>]

At Thu, 9 Dec 2004 09:18:04 +0100 (CET),
Jaroslav wrote:
> 
> On Wed, 8 Dec 2004, Takashi Iwai wrote:
> 
> > At Tue, 7 Dec 2004 23:01:51 +0100,
> > Karsten Wiese wrote:
> > > 
> > > >>>>
> > > Summary: hwdep interface for pcm data.
> > > 
> > > Implements "rawusb" pcm data transfer through hwdep interface:
> > > The usb_hc moves pcm data from/into memory via DMA.
> > > That memory is mmaped by jack's usx2y driver.
> > > Jack's usx2y driver is the first/last executable code to read/write pcm data.
> > > Read/write is a combination of power of 2 period shaping and float/int conversation.
> > > Compared to standard alsa/jack we leave out power of 2 period shaping
> > > inside snd-usb-usx2y which needs memcpy() and additional buffers.
> > > As a side effect possible unwanted pcm-data coruption resulting of
> > > standard alsa's snd-usb-usx2y period shaping scheme falls away.
> > > Result is sane jack operation at buffering schemes down to 128frames, 2 periods.
> > > Also changed Kconfig file, so snd-usb-usx2y is only available for X86, PPC or ALPHA platforms,
> > > as on others DMA-memory isn't mmapable.
> > > 
> > > Signed-off-by: Karsten Wiese <annabellesgarden@yahoo.de>
> > > <<<<
> > 
> > Thanks, applied to the CVS tree now.
> > Please check later whether it works for you...
> 
> My feeling is that it's against all we're trying to do with the PCM 
> interface. Cannot we extend/optimize the current PCM API?

Don't worry, in the new patch, the hwdep does actually only mmap.  The
others are done with the usual PCM API.

The implementation is still a bit tricky, IMO, though.
We can generalize this if there would be more wide needs for such
stuff.


Takashi


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