[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>

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

arch/arm/plat-s3c24xx/dma.c

@@ -1354,18 +1354,22 @@ static inline int is_channel_valid(unsigned int channel)
 	return (channel & DMA_CH_VALID);
 }
 
+static struct s3c24xx_dma_order *dma_order;
+
+
 /* s3c2410_dma_map_channel()
  *
  * turn the virtual channel number into a real, and un-used hardware
  * channel.
  *
- * currently this code uses first-free channel from the specified harware
- * map, not taking into account anything that the board setup code may
- * have to say about the likely peripheral set to be in use.
+ * first, try the dma ordering given to us by either the relevant
+ * dma code, or the board. Then just find the first usable free
+ * channel
 */
 
 struct s3c2410_dma_chan *s3c2410_dma_map_channel(int channel)
 {
+	struct s3c24xx_dma_order_ch *ord = NULL;
 	struct s3c24xx_dma_map *ch_map;
 	struct s3c2410_dma_chan *dmach;
 	int ch;
@@ -1375,6 +1379,27 @@ struct s3c2410_dma_chan *s3c2410_dma_map_channel(int channel)
 
 	ch_map = dma_sel.map + channel;
 
+	/* first, try the board mapping */
+
+	if (dma_order) {
+		ord = &dma_order->channels[channel];
+
+		for (ch = 0; ch < S3C2410_DMA_CHANNELS; ch++) {
+			if (!is_channel_valid(ord->list[ch]))
+				continue;
+
+			if (s3c2410_chans[ord->list[ch]].in_use == 0) {
+				ch = ord->list[ch] & ~DMA_CH_VALID;
+				goto found;
+			}
+		}
+
+		if (ord->flags & DMA_CH_NEVER)
+			return NULL;
+	}
+
+	/* second, search the channel map for first free */
+
 	for (ch = 0; ch < S3C2410_DMA_CHANNELS; ch++) {
 		if (!is_channel_valid(ch_map->channels[ch]))
 			continue;
@@ -1390,6 +1415,7 @@ struct s3c2410_dma_chan *s3c2410_dma_map_channel(int channel)
 
 	/* update our channel mapping */
 
+ found:
 	dmach = &s3c2410_chans[ch];
 	dma_chan_map[channel] = dmach;
 
@@ -1439,3 +1465,20 @@ int __init s3c24xx_dma_init_map(struct s3c24xx_dma_selection *sel)
 
 	return 0;
 }
+
+int __init s3c24xx_dma_order_set(struct s3c24xx_dma_order *ord)
+{
+	struct s3c24xx_dma_order *nord = dma_order;
+
+	if (nord == NULL)
+		nord = kmalloc(sizeof(struct s3c24xx_dma_order), GFP_KERNEL);
+
+	if (nord == NULL) {
+		printk(KERN_ERR "no memory to store dma channel order\n");
+		return -ENOMEM;
+	}
+
+	dma_order = nord;
+	memcpy(nord, ord, sizeof(struct s3c24xx_dma_order));
+	return 0;
+}

include/asm-arm/plat-s3c24xx/dma.h

@@ -14,6 +14,7 @@ extern struct sysdev_class dma_sysclass;
 extern struct s3c2410_dma_chan s3c2410_chans[S3C2410_DMA_CHANNELS];
 
 #define DMA_CH_VALID		(1<<31)
+#define DMA_CH_NEVER		(1<<30)
 
 struct s3c24xx_dma_addr {
 	unsigned long		from;
@@ -43,3 +44,27 @@ struct s3c24xx_dma_selection {
 };
 
 extern int s3c24xx_dma_init_map(struct s3c24xx_dma_selection *sel);
+
+/* struct s3c24xx_dma_order_ch
+ *
+ * channel map for one of the `enum dma_ch` dma channels. the list
+ * entry contains a set of low-level channel numbers, orred with
+ * DMA_CH_VALID, which are checked in the order in the array.
+*/
+
+struct s3c24xx_dma_order_ch {
+	unsigned int	list[S3C2410_DMA_CHANNELS];	/* list of channels */
+	unsigned int	flags;				/* flags */
+};
+
+/* struct s3c24xx_dma_order
+ *
+ * information provided by either the core or the board to give the
+ * dma system a hint on how to allocate channels
+*/
+
+struct s3c24xx_dma_order {
+	struct s3c24xx_dma_order_ch	channels[DMACH_MAX];
+};
+
+extern int s3c24xx_dma_order_set(struct s3c24xx_dma_order *map);