realtek: RTL930x: setup highmem registers during init

For some reason the highmem configuration of RTL930x
devices was totally missed until now. Take over the
setup from the SDK. This will avoid boot stalls on
switches with more than 256 MB RAM when switching
over to kernel 6.18.

Signed-off-by: Markus Stockhausen <[email protected]>
Link: openwrt/openwrt#21327
Signed-off-by: Hauke Mehrtens <[email protected]>

Author: plappermaul

target/linux/realtek/files-6.12/arch/mips/rtl838x/prom.c

@@ -18,7 +18,20 @@
 #include <mach-rtl83xx.h>
 
 #define RTL_SOC_BASE			((volatile void *) 0xB8000000)
+
 #define RTL83XX_DRAM_CONFIG		0x1004
+
+#define RTL9300_SRAMSAR0		0x4000
+#define RTL9300_SRAMSAR1		0x4010
+#define RTL9300_SRAMSAR2		0x4020
+#define RTL9300_SRAMSAR3		0x4030
+#define RTL9300_UMSAR0			0x1300
+#define RTL9300_UMSAR1			0x1310
+#define RTL9300_UMSAR2			0x1320
+#define RTL9300_UMSAR3			0x1330
+#define RTL9300_O0DOR2			0x4220
+#define RTL9300_O0DMAR2			0x4224
+
 #define RTL931X_DRAM_CONFIG		0x14304c
 
 #define soc_r32(reg)			readl(RTL_SOC_BASE + reg)
@@ -251,6 +264,39 @@ static void get_system_memory(void)
 	soc_info.memory_size = 1 << bits;
 }
 
+static void prepare_highmem(void)
+{
+	if ((soc_info.family != RTL9300_FAMILY_ID) ||
+	    (soc_info.memory_size <= 256 * 1024 * 1024) ||
+	    !IS_ENABLED(CONFIG_HIGHMEM))
+		return;
+
+	/*
+	 * To use highmem on RTL930x, SRAM must be deactivated and the highmem mapping
+	 * registers must be setup properly. The hardcoded 0x70000000 might be strange
+	 * but at least it conforms somehow to the RTL931x devices.
+	 *
+	 * - RTL930x: highmem start 0x20000000 + offset 0x70000000 = 0x90000000
+	 * - RTL931x: highmem start 0x90000000 + no offset at all  = 0x90000000
+	 */
+
+	pr_info("highmem kernel on RTL930x with > 256 MB RAM, adapt SoC memory mapping\n");
+
+	soc_w32(0, RTL9300_UMSAR0);
+	soc_w32(0, RTL9300_UMSAR1);
+	soc_w32(0, RTL9300_UMSAR2);
+	soc_w32(0, RTL9300_UMSAR3);
+	soc_w32(0, RTL9300_SRAMSAR0);
+	soc_w32(0, RTL9300_SRAMSAR1);
+	soc_w32(0, RTL9300_SRAMSAR2);
+	soc_w32(0, RTL9300_SRAMSAR3);
+	__sync();
+
+	soc_w32(0x70000000, RTL9300_O0DOR2);
+	soc_w32(0x7fffffff, RTL9300_O0DMAR2);
+	__sync();
+}
+
 void __init prom_init(void)
 {
 	u32 model = read_model();
@@ -261,6 +307,8 @@ void __init prom_init(void)
 
 	pr_info("%s SoC with %d MB\n", get_system_type(), soc_info.memory_size >> 20);
 
+	prepare_highmem();
+
 	/*
 	 * fw_arg2 is be the pointer to the environment. Some devices (e.g. HP JG924A) hand
 	 * over other than expected kernel boot arguments. Something like 0xfffdffff looks