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>

1 files changed, 13 insertions, 7 deletions

diff --git a/arch/blackfin/kernel/cplb-nompu/cplbinit.c b/arch/blackfin/kernel/cplb-nompu/cplbinit.c
index fd9a2f31e686..c9b0a4d53dc1 100644
--- a/arch/blackfin/kernel/cplb-nompu/cplbinit.c
+++ b/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) {