Blackfin: support smaller uncached DMA chunks for memory constrained systems

When working with 8 meg systems, forcing a 1 meg DMA chunk heavily cuts
into the available resources.  So support smaller chunks to better cover
needs for these systems.
Signed-off-by: Barry Song <barry.song@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

arch/blackfin/Kconfig

@@ -896,6 +896,12 @@ config DMA_UNCACHED_2M
 	bool "Enable 2M DMA region"
 config DMA_UNCACHED_1M
 	bool "Enable 1M DMA region"
+config DMA_UNCACHED_512K
+	bool "Enable 512K DMA region"
+config DMA_UNCACHED_256K
+	bool "Enable 256K DMA region"
+config DMA_UNCACHED_128K
+	bool "Enable 128K DMA region"
 config DMA_UNCACHED_NONE
 	bool "Disable DMA region"
 endchoice

arch/blackfin/include/asm/bfin-global.h

@@ -20,6 +20,12 @@
 # define DMA_UNCACHED_REGION (2 * 1024 * 1024)
 #elif defined(CONFIG_DMA_UNCACHED_1M)
 # define DMA_UNCACHED_REGION (1024 * 1024)
+#elif defined(CONFIG_DMA_UNCACHED_512K)
+# define DMA_UNCACHED_REGION (512 * 1024)
+#elif defined(CONFIG_DMA_UNCACHED_256K)
+# define DMA_UNCACHED_REGION (256 * 1024)
+#elif defined(CONFIG_DMA_UNCACHED_128K)
+# define DMA_UNCACHED_REGION (128 * 1024)
 #else
 # define DMA_UNCACHED_REGION (0)
 #endif

arch/blackfin/kernel/cplb-nompu/cplbinit.c

@@ -89,15 +89,25 @@ void __init generate_cplb_tables_cpu(unsigned int cpu)
 
 void __init generate_cplb_tables_all(void)
 {
+	unsigned long uncached_end;
 	int i_d, i_i;
 
 	i_d = 0;
 	/* Normal RAM, including MTD FS.  */
 #ifdef CONFIG_MTD_UCLINUX
-	dcplb_bounds[i_d].eaddr = memory_mtd_start + mtd_size;
+	uncached_end = memory_mtd_start + mtd_size;
 #else
-	dcplb_bounds[i_d].eaddr = memory_end;
+	uncached_end = memory_end;
 #endif
+	/*
+	 * if DMA uncached is less than 1MB, mark the 1MB chunk as uncached
+	 * so that we don't have to use 4kB pages and cause CPLB thrashing
+	 */
+	if ((DMA_UNCACHED_REGION >= 1 * 1024 * 1024) || !DMA_UNCACHED_REGION ||
+	    ((_ramend - uncached_end) >= 1 * 1024 * 1024))
+		dcplb_bounds[i_d].eaddr = uncached_end;
+	else
+		dcplb_bounds[i_d].eaddr = uncached_end & ~(1 * 1024 * 1024);
 	dcplb_bounds[i_d++].data = SDRAM_DGENERIC;
 	/* DMA uncached region.  */
 	if (DMA_UNCACHED_REGION) {
@@ -135,11 +145,7 @@ void __init generate_cplb_tables_all(void)
 
 	i_i = 0;
 	/* Normal RAM, including MTD FS.  */
-#ifdef CONFIG_MTD_UCLINUX
-	icplb_bounds[i_i].eaddr = memory_mtd_start + mtd_size;
-#else
-	icplb_bounds[i_i].eaddr = memory_end;
-#endif
+	icplb_bounds[i_i].eaddr = uncached_end;
 	icplb_bounds[i_i++].data = SDRAM_IGENERIC;
 	/* DMA uncached region.  */
 	if (DMA_UNCACHED_REGION) {