Enable DMA by default in kernel for (S)ATA controllers.

This is needed since some (S)ATA controllers doesn't work properly when
DMA is not activated. When this happens, it prevents to start fossil,
then DMA cannot be enabled from startup scripts. Also, it makes the
first startup much faster when fossil do its initial dump to venti.

An option "*nodma=" was added to plan9.ini to disable DMA if needed.
This option is set in the installation plan9.ini, since the user is
asked to enable or disable DMA at the beginning of the installation
process.

I considered it is preferable to enable DMA by default since most disk
controllers are SATA these days and DMA is part of the specification.
Also, most modern ATA controllers have been known to support DMA
properly.

Optionally, the bootsetup installation script could automatically add
option "*nodma=" in installed plan9.ini when the user choose to
disable DMA.

Reference: /n/sources/patch/maybe/sdata-dma
Date: Thu Apr 14 15:11:05 CES 2011
Signed-off-by: djc@9grid.fr

--- /sys/src/9/pc/sdata.c	Thu Apr 14 15:08:49 2011
+++ /sys/src/9/pc/sdata.c	Thu Apr 14 15:08:43 2011
@@ -571,6 +571,9 @@
 			drive->dma |= 'U'<<16;
 	}
 
+	if(getconf("*nodma") == nil)
+		drive->dmactl = drive->dma;
+
 	return dma;
 }
 
--- /sys/man/8/plan9.ini	Thu Apr 14 15:08:55 2011
+++ /sys/man/8/plan9.ini	Thu Apr 14 15:08:51 2011
@@ -455,6 +455,8 @@
 and
 .I slot
 to use as a root device for bootstrapping.
+.SS \fL*nodma=\fP
+Disable DMA on (S)ATA controllers.
 .SS AUDIO
 .SS \fLaudioX=value\fP
 This defines a sound interface.
--- /sys/lib/dist/pc/plan9.ini	Thu Apr 14 15:09:01 2011
+++ /sys/lib/dist/pc/plan9.ini	Thu Apr 14 15:08:58 2011
@@ -10,6 +10,7 @@
 # will defeat booting from usb devices.
 *nomp=1
 *nobiosload=1
+*nodma=1
 debugboot=1
 # *noahciload=1
 # *debugload=1
--- /sys/lib/dist/pc/plan9.ini.cd	Thu Apr 14 15:09:05 2011
+++ /sys/lib/dist/pc/plan9.ini.cd	Thu Apr 14 15:09:02 2011
@@ -10,6 +10,7 @@
 # will defeat booting from usb devices.
 *nomp=1
 *nobiosload=1
+*nodma=1
 debugboot=1
 # *noahciload=1
 # *debugload=1
--- /sys/lib/dist/pc/plan9.ini.vmware	Thu Apr 14 15:09:09 2011
+++ /sys/lib/dist/pc/plan9.ini.vmware	Thu Apr 14 15:09:06 2011
@@ -4,6 +4,7 @@
 # will defeat booting from usb devices.
 *nomp=1
 *nobiosload=1
+*nodma=1
 debugboot=1
 # *noahciload=1
 # *debugload=1
--- /sys/lib/dist/pc/inst/bootsetup	Thu Apr 14 15:09:14 2011
+++ /sys/lib/dist/pc/inst/bootsetup	Thu Apr 14 15:09:11 2011
@@ -42,6 +42,8 @@
 			echo 'mouseport='^$mouseport
 			echo 'monitor='^$monitor
 			echo 'vgasize='^$vgasize
+			if(! ~ $dmamode yes)
+				echo '*nodma='
 		} >/tmp/plan9.ini
 	}
 	if(! test -f /tmp/plan9ini.bak)