x86: allow CONFIG_ISA_DMA_API to be disabled

Not all 64-bit systems require ISA-style DMA, so allow it to be
configurable.  x86 utilizes the generic ISA DMA allocator from
kernel/dma.c, so require it only when CONFIG_ISA_DMA_API is enabled.

Disabling CONFIG_ISA_DMA_API is dependent on x86_64 since those machines
do not have ISA slots and benefit the most from disabling the option (and
on CONFIG_EXPERT as required by H.  Peter Anvin).

When disabled, this also avoids declaring claim_dma_lock(),
release_dma_lock(), request_dma(), and free_dma() since those interfaces
will no longer be provided.

Signed-off-by: David Rientjes <rientjes@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Bjorn Helgaas <bjorn.helgaas@hp.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: "Luck, Tony" <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/arch/x86/include/asm/dma.h b/arch/x86/include/asm/dma.h
index ca1098a7e58..97b6d8114a4 100644
--- a/arch/x86/include/asm/dma.h
+++ b/arch/x86/include/asm/dma.h
@@ -151,6 +151,7 @@
 #define DMA_AUTOINIT            0x10
 
 
+#ifdef CONFIG_ISA_DMA_API
 extern spinlock_t  dma_spin_lock;
 
 static inline unsigned long claim_dma_lock(void)
@@ -164,6 +165,7 @@ static inline void release_dma_lock(unsigned long flags)
 {
         spin_unlock_irqrestore(&dma_spin_lock, flags);
 }
+#endif /* CONFIG_ISA_DMA_API */
 
 /* enable/disable a specific DMA channel */
 static inline void enable_dma(unsigned int dmanr)
@@ -303,9 +305,11 @@ static inline int get_dma_residue(unsigned int dmanr)
 }
 
 
-/* These are in kernel/dma.c: */
+/* These are in kernel/dma.c because x86 uses CONFIG_GENERIC_ISA_DMA */
+#ifdef CONFIG_ISA_DMA_API
 extern int request_dma(unsigned int dmanr, const char *device_id);
 extern void free_dma(unsigned int dmanr);
+#endif
 
 /* From PCI */