[ARM] 4177/1: S3C24XX: Add DMA channel allocation order
Allow the CPU code, and any board specific initialisation
code to change the allocation order of the DMA channels,
or stop a peripheral allocating any DMA at-all.
This is due to the scarce mapping of DMA channels on
some earlier S3C24XX cpus, where the selection changes
depending on the channel in use.
Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/Documentation/arm/Samsung-S3C24XX/DMA.txt b/Documentation/arm/Samsung-S3C24XX/DMA.txt
new file mode 100644
index 0000000..37f4edc
--- /dev/null
+++ b/Documentation/arm/Samsung-S3C24XX/DMA.txt
@@ -0,0 +1,46 @@
+ S3C2410 DMA
+ ===========
+
+Introduction
+------------
+
+ The kernel provides an interface to manage DMA transfers
+ using the DMA channels in the cpu, so that the central
+ duty of managing channel mappings, and programming the
+ channel generators is in one place.
+
+
+DMA Channel Ordering
+--------------------
+
+ Many of the range do not have connections for the DMA
+ channels to all sources, which means that some devices
+ have a restricted number of channels that can be used.
+
+ To allow flexibilty for each cpu type and board, the
+ dma code can be given an dma ordering structure which
+ allows the order of channel search to be specified, as
+ well as allowing the prohibition of certain claims.
+
+ struct s3c24xx_dma_order has a list of channels, and
+ each channel within has a slot for a list of dma
+ channel numbers. The slots are searched in order, for
+ the presence of a dma channel number with DMA_CH_VALID
+ orred in.
+
+ If the order has the flag DMA_CH_NEVER set, then after
+ checking the channel list, the system will return no
+ found channel, thus denying the request.
+
+ A board support file can call s3c24xx_dma_order_set()
+ to register an complete ordering set. The routine will
+ copy the data, so the original can be discared with
+ __initdata.
+
+
+Authour
+-------
+
+Ben Dooks,
+Copyright (c) 2007 Ben Dooks, Simtec Electronics
+Licensed under the GPL v2