ARC: [plat-eznps] Use dedicated user stack top
NPS use special mapping right below TASK_SIZE.
Hence we need to lower STACK_TOP so that user stack won't
overlap NPS special mapping.
Signed-off-by: Noam Camus <noamc@ezchip.com>
Acked-by: Vineet Gupta <vgupta@synopsys.com>
diff --git a/arch/arc/include/asm/processor.h b/arch/arc/include/asm/processor.h
index d0a9211..194a09f 100644
--- a/arch/arc/include/asm/processor.h
+++ b/arch/arc/include/asm/processor.h
@@ -121,7 +121,25 @@
#define USER_KERNEL_GUTTER (VMALLOC_START - TASK_SIZE)
+#ifdef CONFIG_ARC_PLAT_EZNPS
+/* NPS architecture defines special window of 129M in user address space for
+ * special memory areas, when accessing this window the MMU do not use TLB.
+ * Instead MMU direct the access to:
+ * 0x57f00000:0x57ffffff -- 1M of closely coupled memory (aka CMEM)
+ * 0x58000000:0x5fffffff -- 16 huge pages, 8M each, with fixed map (aka FMTs)
+ *
+ * CMEM - is the fastest memory we got and its size is 16K.
+ * FMT - is used to map either to internal/external memory.
+ * Internal memory is the second fast memory and its size is 16M
+ * External memory is the biggest memory (16G) and also the slowest.
+ *
+ * STACK_TOP need to be PMD align (21bit) that is why we supply 0x57e00000.
+ */
+#define STACK_TOP 0x57e00000
+#else
#define STACK_TOP TASK_SIZE
+#endif
+
#define STACK_TOP_MAX STACK_TOP
/* This decides where the kernel will search for a free chunk of vm