[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>

1 files changed, 46 insertions, 0 deletions

diff --git a/Documentation/arm/Samsung-S3C24XX/DMA.txt b/Documentation/arm/Samsung-S3C24XX/DMA.txt
new file mode 100644
index 000000000000..37f4edcc5d87
--- /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