[PATCH] Fix up SH DMAC code to correctly handle PVR DMA

[Adrian McMenamin <adrian@newgolddream.dyndns.info>]

This patch fixes up SH DMAC code to correctly handle channel 2 DMA on
the Dreamcast.

Points to note:

* Currently the comments say that dar must be set - this appears to be
incorrect
* Currently the code uses calc_xmit_shift(chan) though that fuction does
not appear to work - this code relies on a division by 32 before the
xfer function is called
* Currently the code supports reading and writing, but the hardware only
supports writing

Signed-off by Adrian McMenamin <adrian@mcmen.demon.co.uk>

--- arch/sh/drivers/dma/dma-sh.c	2007/09/22 18:34:42	1.1
+++ arch/sh/drivers/dma/dma-sh.c	2007/09/22 18:37:28	1.2
@@ -150,6 +150,13 @@ static void sh_dmac_disable_dma(struct d
 
 static int sh_dmac_xfer_dma(struct dma_channel *chan)
 {
+	/* Handle Dreamcast PVR cascade */
+	if (mach_is_dreamcast() && chan->chan == PVR2_CASCADE_CHAN)
+	{
+		ctrl_outl(chan->sar, SAR[chan->chan]);
+		ctrl_outl(chan->count, DMATCR[chan->chan]);
+		return 0;
+	}
 	/*
 	 * If we haven't pre-configured the channel with special flags, use
 	 * the defaults.
@@ -159,26 +166,9 @@ static int sh_dmac_xfer_dma(struct dma_c
 
 	sh_dmac_disable_dma(chan);
 
-	/*
-	 * Single-address mode usage note!
-	 *
-	 * It's important that we don't accidentally write any value to SAR/DAR
-	 * (this includes 0) that hasn't been directly specified by the user if
-	 * we're in single-address mode.
-	 *
-	 * In this case, only one address can be defined, anything else will
-	 * result in a DMA address error interrupt (at least on the SH-4),
-	 * which will subsequently halt the transfer.
-	 *
-	 * Channel 2 on the Dreamcast is a special case, as this is used for
-	 * cascading to the PVR2 DMAC. In this case, we still need to write
-	 * SAR and DAR, regardless of value, in order for cascading to work.
-	 */
-	if (chan->sar || (mach_is_dreamcast() &&
-			  chan->chan == PVR2_CASCADE_CHAN))
+	if (chan->sar)
 		ctrl_outl(chan->sar, SAR[chan->chan]);
-	if (chan->dar || (mach_is_dreamcast() &&
-			  chan->chan == PVR2_CASCADE_CHAN))
+	if (chan->dar)
 		ctrl_outl(chan->dar, DAR[chan->chan]);
 
 	ctrl_outl(chan->count >> calc_xmit_shift(chan), DMATCR[chan->chan]);