Re: [PATCH] Fix SH DMAC code to handle PVR2 cascade

[Paul Mundt <lethal@linux-sh.org>]

On Tue, Oct 02, 2007 at 10:09:27PM +0100, Adrian McMenamin wrote:
> Fix SH DMAC code to correctly handle PVR2 cascade DMA.
> 
> This updates http://lkml.org/lkml/2007/10/2/276
> 
> (I decided it was better to have the true size of the transfer put in
> via the API and refactor this here. And calc_xmit_shift(chan) should
> return 5 but only returns 3 so I've not used it here)
> 
It would be helpful to know why calc_xmit_shift() is broken here rather
than just coding around it, as this will have implications for the other
DMA channels on SH7091/SH7750.

Now that you've completely bypassed the rest of the SH-DMAC ->xfer_dma()
op, it's clear that the existing infrastructure needs a bit of rework for
dealing with the cascaded DMACs (especially for single-address mode only,
unidirectionally). It would be nice to get the mach-specific kludges for
cascade out of dma-sh entirely.

This can certainly be fixed for 2.6.24, though a larger overhaul is
2.6.25 material at this point.