powerpc/32: drop unused ISA_DMA_THRESHOLD

The ISA_DMA_THRESHOLD variable is set by several platforms but never
referenced.
Remove it.

Signed-off-by: Mike Rapoport <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/powerpc/include/asm/dma.h

···
 #define DMA2_EXT_REG		0x4D6
 
 #ifndef __powerpc64__
-    /* in arch/ppc/kernel/setup.c -- Cort */
+    /* in arch/powerpc/kernel/setup_32.c -- Cort */
     extern unsigned int DMA_MODE_WRITE;
     extern unsigned int DMA_MODE_READ;
-    extern unsigned long ISA_DMA_THRESHOLD;
 #else
     #define DMA_MODE_READ	0x44	/* I/O to memory, no autoinit, increment, single mode */
     #define DMA_MODE_WRITE	0x48	/* memory to I/O, no autoinit, increment, single mode */

arch/powerpc/kernel/setup_32.c

···
 int smp_hw_index[NR_CPUS];
 EXPORT_SYMBOL(smp_hw_index);
 
-unsigned long ISA_DMA_THRESHOLD;
 unsigned int DMA_MODE_READ;
 unsigned int DMA_MODE_WRITE;
 

arch/powerpc/platforms/44x/warp.c

···
 	if (!of_machine_is_compatible("pika,warp"))
 		return 0;
 
-	/* For arch_dma_alloc */
-	ISA_DMA_THRESHOLD = ~0L;
-
 	return 1;
 }
 

arch/powerpc/platforms/52xx/efika.c

···
 	if (strcmp(model, "EFIKA5K2"))
 		return 0;
 
-	ISA_DMA_THRESHOLD = ~0L;
 	DMA_MODE_READ = 0x44;
 	DMA_MODE_WRITE = 0x48;
 

arch/powerpc/platforms/amigaone/setup.c

···
 		 */
 		cur_cpu_spec->cpu_features &= ~CPU_FTR_NEED_COHERENT;
 
-		ISA_DMA_THRESHOLD = 0x00ffffff;
 		DMA_MODE_READ = 0x44;
 		DMA_MODE_WRITE = 0x48;
 

arch/powerpc/platforms/chrp/setup.c

···
  	if (strcmp(dtype, "chrp"))
 		return 0;
 
-	ISA_DMA_THRESHOLD = ~0L;
 	DMA_MODE_READ = 0x44;
 	DMA_MODE_WRITE = 0x48;
 

arch/powerpc/platforms/powermac/setup.c

···
 
 #ifdef CONFIG_PPC32
 	/* isa_io_base gets set in pmac_pci_init */
-	ISA_DMA_THRESHOLD = ~0L;
 	DMA_MODE_READ = 1;
 	DMA_MODE_WRITE = 2;
 #endif /* CONFIG_PPC32 */