Re: [PATCH 1/7] [RFC] OMAP: MCBSP: hwmod database for 2xxx devices

[Peter Ujfalusi <peter.ujfalusi@nokia.com>]

On Thursday 14 October 2010 17:51:15 ext Varadarajan, Charulatha wrote:

> > Yes, this need to be fixed, but it can be done later, it does
> > not need to be
> > part of the hwmod series.
> 
> Okay.

This problem there for a long time, and so far no one complained, or fixed it.
Probably there are no users for pollread/write at all, but I would not remove 
the functionality. It is better to fix them later.
 
> > > 2. DMA transfers would also not work as it requires a patch
> > 
> > similar to [y].
> > 
> > Well, this patch was sent in 2008. nowdays we moved the OMAP
> > audio support to
> > ASoC, and there are no 'legacy' ALSA arm/omap drivers anymore.
> > In ASoC the cpu_dai and the platform drivers are separate things.
> > This allows us to use the same platform driver (omap-pcm) for
> > McBSp, McPDM (and
> > in theory we could have OMAP2 EAC) cpu_dai drivers without
> > duplicating code.
> > As a note: most of the features this patch was trying to
> > implement is already
> > done for the ASoC implementation, but if there is need for
> > new features, it has
> > to be done using the ASoC framework.
> 
> If we do this, would it not contradict the idea of keeping the door
> open for others to use the McBSP ports?

Why? If you add support for different sample formats to ASoC, it will not change 
anything.
 
> If other users should be allowed to use McBSP ports, it is good to
> have DMA support in plat-omap/mcbsp.c itself and modify the asoc
> implementation to take advantage of the proposed new mcbsp
> design. If agreed, this shall be addressed later. Please let
> me know your thoughts on this.

What I mean is that later we could add DMA transfer functionality if there is a 
need, but at the moment I don't see any reason to do that.
Also moving the DMA functionality to plat-omap/mcbsp.c would require quite a big 
change in there, and as well in the ASoC code. On top of that we will broke the 
sound/soc/omap/omap-pcm.c to be McBSP independent, and that is one of the main 
points here. We are using omap-pcm.c with McBSP and McPDM dai drivers. That has 
to remain the same.
In the future we can implement DMA transfer capabilities to mcbsp.
I would not do this as part of hwmod either.
I think such an extension to the current McBSP code is only needed if/when we 
have other users for McBSP than audio.

> > > Coming back to the original question. Either we need to fix
> > 
> > the broken
> > 
> > > legacy mcbsp driver or move the omap-mcbsp driver completely to asoc
> > > layer. What do you say?
> > 
> > I would keep the partitioning same as it is now.
> 
> Okay.
> 
> > If there is a reason we can add bus driver functionality to
> > McBSP,
> 
> Can you elaborate? mcbsp driver is already following platform bus
> device model.

I meant adding DMA functionality to McBSP. I would not worry about this at this 
time.

> 
> > but at the
> > moment there is no need for that.
> 
> For testing any changes in mcbsp driver (including hwmod), we are
> relying on internal patches (dma/pollmode patches). Instead, if
> mcbsp dma support is available in the driver itself, it would be
> useful for bug fixing/development activities.

You should use audio (ASoC) for verification, for example Beagle, or other 
board. I would say that the audio support is solid on OMAP platforms, and that 
is the main thing which must work after hwmod conversion.

-- 
Péter