Building of arch/arm/plat-mxc/ssi-fiq.S failed w/ THUMB2 enabled?

[s.hauer@pengutronix.de (Sascha Hauer)]

On Wed, Jan 25, 2012 at 02:34:18PM +0000, Russell King - ARM Linux wrote:
> On Wed, Jan 25, 2012 at 08:06:03AM -0600, Matt Sealey wrote:
> > On Mon, Jan 23, 2012 at 5:59 AM, Sascha Hauer <s.hauer@pengutronix.de> wrote:
> > > On Fri, Jan 20, 2012 at 12:00:03PM +0000, Dave Martin wrote:
> > >> On Fri, Jan 20, 2012 at 11:52:17AM +0000, Russell King - ARM Linux wrote:
> > >> > On Fri, Dec 02, 2011 at 11:24:18AM +0100, Uwe Kleine-K?nig wrote:
> > >> > > On Fri, Dec 02, 2011 at 06:01:08PM +0800, Eric Miao wrote:
> > >> > > > Hi Dave & Sascha,
> > >> > > >
> > >> > > > I checked the log of this file, found a THUMB2 related changes, yet
> > >> > > > I'm still having the failure below, can you help do a quick check?
> > >> > > the problem is that in Thumb most commands don't work with r8-r15
> > >> > > because there are only three bits used to encode them. This is
> > >> > > unfortunate as the other registers are not banked for FIQ.
> > >> > >
> > >> > > The best possibility I see is to save some unbanked registers to the
> > >> > > banked registers on entry and restore them on exception exit.
> > >> >
> > >> > Or always build this as ARM code.
> > >>
> > >> That should work, sure -- I prefer to keep the number of instances where
> > >> we need to do this to a minimum if we can, though.
> > >
> > > I vote for compiling this in ARM mode since it's a straight forward
> > > solution.
> > >
> > > Some background:
> > >
> > > The original reason for creating this code was that we did not have SDMA
> > > support at the time I wanted audio support. The FIQ code was a simple
> > > way to seperate audio and DMA support and to push them to mainline
> > > seperately. There is another reason for having this code though. The
> > > i.MX SSI port is quite broken in AC97 mode. Some AC97 codecs like the
> > > WM9712 always send data in slot 12 (IIRC it contains gpio status). The
> > > SSI unit always puts all valid slots into the data stream, so we end up
> > > having the audio rx data interleaved with the gpio status data. The FIQ
> > > code is used to skip the gpio status data (see /* dummy read to skip
> > > slot 12 */ in ssi-fiq.S).
> > 
> > Okay so let's start with the thumb-isation of that code since it's
> > breaking thumb2 kernel builds for i.MX with
> > SSI audio (regardless of AC97 requirement).
> 
> Well, there's two solutions to this:
> 
> - we declare that it's obsolete now that SDMA support is in place.
> - we always build the code in ARM mode.

The latter please. As mentioned it is still necessary for AC97 mode and
used at least on the pcm043 board.

Sascha

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