ARC: mm: Decouple RAM base address from kernel link address

	[Needed for HSDK]

Currently the first page of system (hence RAM base) is assumed to be
@ CONFIG_LINUX_LINK_BASE, where kernel itself is linked.

However is case of HSDK platform, for reasons explained in that patch,
this is not true. kernel needs to be linked @ 0x9000_0000 while DDR
is still wired at 0x8000_0000. To properly account for this 256M of RAM,
we need to introduce a new option and base page frame accountiing off of
it.
Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
[vgupta: renamed  CONFIG_KERNEL_RAM_BASE_ADDRESS => CONFIG_LINUX_RAM_BASE
       : simplified changelog]

arch/arc/Kconfig

@@ -418,7 +418,7 @@ endif	# ISA_ARCV2
 endmenu   # "ARC CPU Configuration"
 
 config LINUX_LINK_BASE
-	hex "Linux Link Address"
+	hex "Kernel link address"
 	default "0x80000000"
 	help
 	  ARC700 divides the 32 bit phy address space into two equal halves
@@ -431,6 +431,14 @@ config LINUX_LINK_BASE
 	  If you don't know what the above means, leave this setting alone.
 	  This needs to match memory start address specified in Device Tree
 
+config LINUX_RAM_BASE
+	hex "RAM base address"
+	default LINUX_LINK_BASE
+	help
+	  By default Linux is linked at base of RAM. However in some special
+	  cases (such as HSDK), Linux can't be linked at start of DDR, hence
+	  this option.
+
 config HIGHMEM
 	bool "High Memory Support"
 	select ARCH_DISCONTIGMEM_ENABLE

arch/arc/boot/dts/axc001.dtsi

@@ -99,7 +99,7 @@ mb_intc: dw-apb-ictl@0xe0012000 {
 
 	memory {
 		device_type = "memory";
-		/* CONFIG_KERNEL_RAM_BASE_ADDRESS needs to match low mem start */
+		/* CONFIG_LINUX_RAM_BASE needs to match low mem start */
 		reg = <0x0 0x80000000 0x0 0x1b000000>;	/* (512 - 32) MiB */
 	};
 

arch/arc/boot/dts/axc003.dtsi

@@ -109,7 +109,7 @@ mb_intc: dw-apb-ictl@0xe0012000 {
 
 	memory {
 		device_type = "memory";
-		/* CONFIG_KERNEL_RAM_BASE_ADDRESS needs to match low mem start */
+		/* CONFIG_LINUX_RAM_BASE needs to match low mem start */
 		reg = <0x0 0x80000000 0x0 0x20000000	/* 512 MiB low mem */
 		       0x1 0xc0000000 0x0 0x40000000>;	/* 1 GiB highmem */
 	};

arch/arc/boot/dts/axc003_idu.dtsi

@@ -115,7 +115,7 @@ mb_intc: dw-apb-ictl@0xe0012000 {
 
 	memory {
 		device_type = "memory";
-		/* CONFIG_KERNEL_RAM_BASE_ADDRESS needs to match low mem start */
+		/* CONFIG_LINUX_RAM_BASE needs to match low mem start */
 		reg = <0x0 0x80000000 0x0 0x20000000	/* 512 MiB low mem */
 		       0x1 0xc0000000 0x0 0x40000000>;	/* 1 GiB highmem */
 	};

arch/arc/boot/dts/nsim_hs.dts

@@ -18,7 +18,7 @@ / {
 
 	memory {
 		device_type = "memory";
-		/* CONFIG_LINUX_LINK_BASE needs to match low mem start */
+		/* CONFIG_LINUX_RAM_BASE needs to match low mem start */
 		reg = <0x0 0x80000000 0x0 0x20000000	/* 512 MB low mem */
 		       0x1 0x00000000 0x0 0x40000000>;	/* 1 GB highmem */
 	};

arch/arc/include/asm/page.h

@@ -85,7 +85,7 @@ typedef pte_t * pgtable_t;
  */
 #define virt_to_pfn(kaddr)	(__pa(kaddr) >> PAGE_SHIFT)
 
-#define ARCH_PFN_OFFSET		virt_to_pfn(CONFIG_LINUX_LINK_BASE)
+#define ARCH_PFN_OFFSET		virt_to_pfn(CONFIG_LINUX_RAM_BASE)
 
 #ifdef CONFIG_FLATMEM
 #define pfn_valid(pfn)		(((pfn) - ARCH_PFN_OFFSET) < max_mapnr)

arch/arc/mm/cache.c

@@ -1173,7 +1173,7 @@ noinline void __init arc_ioc_setup(void)
 	write_aux_reg(ARC_REG_IO_COH_AP0_SIZE, order_base_2(mem_sz >> 10) - 2);
 
 	/* for now assume kernel base is start of IOC aperture */
-	ioc_base = CONFIG_LINUX_LINK_BASE;
+	ioc_base = CONFIG_LINUX_RAM_BASE;
 
 	if (ioc_base % mem_sz != 0)
 		panic("IOC Aperture start must be aligned to the size of the aperture");

arch/arc/mm/init.c

@@ -26,7 +26,7 @@ pgd_t swapper_pg_dir[PTRS_PER_PGD] __aligned(PAGE_SIZE);
 char empty_zero_page[PAGE_SIZE] __aligned(PAGE_SIZE);
 EXPORT_SYMBOL(empty_zero_page);
 
-static const unsigned long low_mem_start = CONFIG_LINUX_LINK_BASE;
+static const unsigned long low_mem_start = CONFIG_LINUX_RAM_BASE;
 static unsigned long low_mem_sz;
 
 #ifdef CONFIG_HIGHMEM
@@ -63,7 +63,7 @@ void __init early_init_dt_add_memory_arch(u64 base, u64 size)
 
 	if (!low_mem_sz) {
 		if (base != low_mem_start)
-			panic("CONFIG_LINUX_LINK_BASE != DT memory { }");
+			panic("CONFIG_LINUX_RAM_BASE != DT memory { }");
 
 		low_mem_sz = size;
 		in_use = 1;
@@ -161,7 +161,7 @@ void __init setup_arch_memory(void)
 	 * We can't use the helper free_area_init(zones[]) because it uses
 	 * PAGE_OFFSET to compute the @min_low_pfn which would be wrong
 	 * when our kernel doesn't start at PAGE_OFFSET, i.e.
-	 * PAGE_OFFSET != CONFIG_LINUX_LINK_BASE
+	 * PAGE_OFFSET != CONFIG_LINUX_RAM_BASE
 	 */
 	free_area_init_node(0,			/* node-id */
 			    zones_size,		/* num pages per zone */