isa: set 24-bit dma_mask for ISA devices

dma_alloc_coherent() on x86 currently takes a passed in NULL device
pointer to mean that it should allocate an ISA compatible (24-bit) buffer
which is a bit of a hack.

The ALSA ISA drivers are the main consumers of this but have a struct
device in fact readily available.

For the legacy drivers, this sets the device dma_mask in preparation for
using the actual device with the DMA API so as to eventually not need the
NULL hack in dma_alloc_coherent().

This does not fix a current bug -- 2.6.26-rc1 stumbled over the NULL hack
in dma_alloc_coherent() but this has already been fixed in commit
4a367f3a9dbf2e7ffcee4702203479809236ee6e by Takashi Iwai.

Signed-off-by: Rene Herman <rene.herman@gmail.com>
Cc: Bjorn Helgaas <bjorn.helgaas@hp.com>
Acked-by: Takashi Iwai <tiwai@suse.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/base/isa.c

@@ -7,6 +7,7 @@
 #include <linux/slab.h>
 #include <linux/module.h>
 #include <linux/init.h>
+#include <linux/dma-mapping.h>
 #include <linux/isa.h>
 
 static struct device isa_bus = {
@@ -141,6 +142,9 @@ int isa_register_driver(struct isa_driver *isa_driver, unsigned int ndev)
 		isa_dev->dev.release		= isa_dev_release;
 		isa_dev->id			= id;
 
+		isa_dev->dev.coherent_dma_mask = DMA_24BIT_MASK;
+		isa_dev->dev.dma_mask = &isa_dev->dev.coherent_dma_mask;
+
 		error = device_register(&isa_dev->dev);
 		if (error) {
 			put_device(&isa_dev->dev);