ramips: mt7621: add support for memory detection

mt7621 has the following memory map:
0x0-0x1c000000: lower 448m memory
0x1c000000-0x2000000: peripheral registers
0x20000000-0x2400000: higher 64m memory

detect_memory_region in arch/mips/kernel/setup.c only add the first
memory region and isn't suitable for 512m memory detection because
it may accidentally read the memory area for peripheral registers.

This commit adds memory detection capability for mt7621:
1. add the highmem area when 512m is detected.
2. guard memcmp from accessing peripheral registers:
     This only happens when some weird user decided to change
     kernel load address to 256m or higher address. Since this
     is a quite unusual case, we just skip 512m testing and return
     256m as memory size.

Signed-off-by: Chuanhong Guo <[email protected]>

target/linux/ramips/patches-4.14/105-mt7621-memory-detect.patch

@@ -0,0 +1,125 @@
+From b5a52351a66f3c2a7a207548aa87d78ff2d336c0 Mon Sep 17 00:00:00 2001
+From: Chuanhong Guo <[email protected]>
+Date: Wed, 10 Jul 2019 00:24:48 +0800
+Subject: [PATCH] MIPS: ralink: mt7621: add memory detection support
+
+mt7621 has the following memory map:
+0x0-0x1c000000: lower 448m memory
+0x1c000000-0x2000000: peripheral registers
+0x20000000-0x2400000: higher 64m memory
+
+detect_memory_region in arch/mips/kernel/setup.c only add the first
+memory region and isn't suitable for 512m memory detection because
+it may accidentally read the memory area for peripheral registers.
+
+This commit adds memory detection capability for mt7621:
+1. add the highmem area when 512m is detected.
+2. guard memcmp from accessing peripheral registers:
+     This only happens when some weird user decided to change
+     kernel load address to 256m or higher address. Since this
+     is a quite unusual case, we just skip 512m testing and return
+     256m as memory size.
+
+Signed-off-by: Chuanhong Guo <[email protected]>
+---
+ arch/mips/include/asm/mach-ralink/mt7621.h |  7 ++---
+ arch/mips/ralink/mt7621.c                  | 30 +++++++++++++++++++---
+ 2 files changed, 30 insertions(+), 7 deletions(-)
+
+--- a/arch/mips/include/asm/mach-ralink/mt7621.h
++++ b/arch/mips/include/asm/mach-ralink/mt7621.h
+@@ -46,9 +46,10 @@
+ #define CPU_PLL_FBDIV_MASK		0x7f
+ #define CPU_PLL_FBDIV_SHIFT		4
+ 
+-#define MT7621_DRAM_BASE                0x0
+-#define MT7621_DDR2_SIZE_MIN		32
+-#define MT7621_DDR2_SIZE_MAX		256
++#define MT7621_LOWMEM_BASE		0x0
++#define MT7621_LOWMEM_MAX_SIZE		0x1C000000
++#define MT7621_HIGHMEM_BASE		0x20000000
++#define MT7621_HIGHMEM_SIZE		0x4000000
+ 
+ #define MT7621_CHIP_NAME0		0x3637544D
+ #define MT7621_CHIP_NAME1		0x20203132
+--- a/arch/mips/ralink/mt7621.c
++++ b/arch/mips/ralink/mt7621.c
+@@ -15,6 +15,7 @@
+ #include <linux/clk-provider.h>
+ #include <dt-bindings/clock/mt7621-clk.h>
+ 
++#include <asm/bootinfo.h>
+ #include <asm/mipsregs.h>
+ #include <asm/smp-ops.h>
+ #include <asm/mips-cps.h>
+@@ -57,6 +58,8 @@
+ #define MT7621_GPIO_MODE_SDHCI_SHIFT	18
+ #define MT7621_GPIO_MODE_SDHCI_GPIO	1
+ 
++static void *detect_magic __initdata = detect_memory_region;
++
+ static struct rt2880_pmx_func uart1_grp[] =  { FUNC("uart1", 0, 1, 2) };
+ static struct rt2880_pmx_func i2c_grp[] =  { FUNC("i2c", 0, 3, 2) };
+ static struct rt2880_pmx_func uart3_grp[] = {
+@@ -141,6 +144,28 @@ static struct clk *__init mt7621_add_sys
+ 	return clk;
+ }
+ 
++void __init mt7621_memory_detect(void)
++{
++	void *dm = &detect_magic;
++	phys_addr_t size;
++
++	for (size = 32 * SZ_1M; size < 256 * SZ_1M; size <<= 1) {
++		if (!memcmp(dm, dm + size, sizeof(detect_magic)))
++			break;
++	}
++
++	if ((size == 256 * SZ_1M) &&
++	    (CPHYSADDR(dm + size) < MT7621_LOWMEM_MAX_SIZE) &&
++	    memcmp(dm, dm + size, sizeof(detect_magic))) {
++		add_memory_region(MT7621_LOWMEM_BASE, MT7621_LOWMEM_MAX_SIZE,
++				  BOOT_MEM_RAM);
++		add_memory_region(MT7621_HIGHMEM_BASE, MT7621_HIGHMEM_SIZE,
++				  BOOT_MEM_RAM);
++	} else {
++		add_memory_region(MT7621_LOWMEM_BASE, size, BOOT_MEM_RAM);
++	}
++}
++
+ void __init ralink_clk_init(void)
+ {
+ 	u32 syscfg, xtal_sel, clkcfg, clk_sel, curclk, ffiv, ffrac;
+@@ -319,10 +344,7 @@ void prom_soc_init(struct ralink_soc_inf
+ 		(rev >> CHIP_REV_VER_SHIFT) & CHIP_REV_VER_MASK,
+ 		(rev & CHIP_REV_ECO_MASK));
+ 
+-	soc_info->mem_size_min = MT7621_DDR2_SIZE_MIN;
+-	soc_info->mem_size_max = MT7621_DDR2_SIZE_MAX;
+-	soc_info->mem_base = MT7621_DRAM_BASE;
+-
++	soc_info->mem_detect = mt7621_memory_detect;
+ 	rt2880_pinmux_data = mt7621_pinmux_data;
+ 
+ 
+--- a/arch/mips/ralink/common.h
++++ b/arch/mips/ralink/common.h
+@@ -19,6 +19,7 @@ struct ralink_soc_info {
+ 	unsigned long mem_size;
+ 	unsigned long mem_size_min;
+ 	unsigned long mem_size_max;
++	void (*mem_detect)(void);
+ };
+ extern struct ralink_soc_info soc_info;
+ 
+--- a/arch/mips/ralink/of.c
++++ b/arch/mips/ralink/of.c
+@@ -89,6 +89,8 @@ void __init plat_mem_setup(void)
+ 	of_scan_flat_dt(early_init_dt_find_memory, NULL);
+ 	if (memory_dtb)
+ 		of_scan_flat_dt(early_init_dt_scan_memory, NULL);
++	else if (soc_info.mem_detect)
++		soc_info.mem_detect();
+ 	else if (soc_info.mem_size)
+ 		add_memory_region(soc_info.mem_base, soc_info.mem_size * SZ_1M,
+ 				  BOOT_MEM_RAM);