[PATCH] mips: vcoreiii: Fix cache coherency issues

[Lars Povlsen]

This patch fixes an stability issue seen on some vcoreiii targets,
which was root caused to a cache inconsistency situation.

The inconsistency was caused by having kuseg pointing to NOR area but
used as a stack/gd/heap area during initialization, while only
relatively late remapping the RAM area into kuseg position.

The fix is to initialize the DDR right after the TLB setup, and then
remapping it into position before gd/stack/heap usage.

Reported-by: Ramin Seyed-Moussavi <ramin.moussavi at yacoub.de>
Reviewed-by: Alexandre Belloni <alexandre.belloni at bootlin.com>
Reviewed-by: Horatiu Vultur <horatiu.vultur at microchip.com>
Signed-off-by: Lars Povlsen <lars.povlsen at microchip.com>
---
 arch/mips/mach-mscc/cpu.c              |  9 +++++----
 arch/mips/mach-mscc/dram.c             | 14 +++++---------
 arch/mips/mach-mscc/include/mach/ddr.h |  4 ----
 arch/mips/mach-mscc/lowlevel_init.S    | 17 ++++++++++++++++-
 4 files changed, 26 insertions(+), 18 deletions(-)

diff --git a/arch/mips/mach-mscc/cpu.c b/arch/mips/mach-mscc/cpu.c
index ac75d51da5..3ee589891b 100644
--- a/arch/mips/mach-mscc/cpu.c
+++ b/arch/mips/mach-mscc/cpu.c
@@ -7,6 +7,7 @@
 
 #include <asm/io.h>
 #include <asm/types.h>
+#include <asm/mipsregs.h>
 
 #include <mach/tlb.h>
 #include <mach/ddr.h>
@@ -53,7 +54,6 @@ void vcoreiii_tlb_init(void)
 		   MMU_REGIO_RW);
 #endif
 
-#if  CONFIG_SYS_TEXT_BASE == MSCC_FLASH_TO
 	/*
 	 * If U-Boot is located in NOR then we want to be able to use
 	 * the data cache in order to boot in a decent duration
@@ -71,9 +71,10 @@ void vcoreiii_tlb_init(void)
 	create_tlb(tlbix++, MSCC_DDR_TO, MSCC_RAM_TLB_SIZE, MMU_REGIO_RW,
 		   MSCC_ATTRIB2);
 
-	/* Enable caches by clearing the bit ERL, which is set on reset */
-	write_c0_status(read_c0_status() & ~BIT(2));
-#endif /* CONFIG_SYS_TEXT_BASE */
+	/* Enable mapping (using TLB) kuseg by clearing the bit ERL,
+	 * which is set on reset.
+	 */
+	write_c0_status(read_c0_status() & ~ST0_ERL);
 }
 
 int mach_cpu_init(void)
diff --git a/arch/mips/mach-mscc/dram.c b/arch/mips/mach-mscc/dram.c
index c43f7a585b..72c70c9e84 100644
--- a/arch/mips/mach-mscc/dram.c
+++ b/arch/mips/mach-mscc/dram.c
@@ -31,7 +31,7 @@ static inline int vcoreiii_train_bytelane(void)
 
 int vcoreiii_ddr_init(void)
 {
-	int res;
+	register int res;
 
 	if (!(readl(BASE_CFG + ICPU_MEMCTRL_STAT)
 	      & ICPU_MEMCTRL_STAT_INIT_DONE)) {
@@ -40,20 +40,19 @@ int vcoreiii_ddr_init(void)
 		if (hal_vcoreiii_init_dqs() || vcoreiii_train_bytelane())
 			hal_vcoreiii_ddr_failed();
 	}
-#if (CONFIG_SYS_TEXT_BASE != 0x20000000)
+
 	res = dram_check();
 	if (res == 0)
 		hal_vcoreiii_ddr_verified();
 	else
 		hal_vcoreiii_ddr_failed();
 
-	/* Clear boot-mode and read-back to activate/verify */
+	/*  Remap DDR to kuseg: Clear boot-mode */
 	clrbits_le32(BASE_CFG + ICPU_GENERAL_CTRL,
 		     ICPU_GENERAL_CTRL_BOOT_MODE_ENA);
+	/* - and read-back to activate/verify */
 	readl(BASE_CFG + ICPU_GENERAL_CTRL);
-#else
-	res = 0;
-#endif
+
 	return res;
 }
 
@@ -66,9 +65,6 @@ int print_cpuinfo(void)
 
 int dram_init(void)
 {
-	while (vcoreiii_ddr_init())
-		;
-
 	gd->ram_size = CONFIG_SYS_SDRAM_SIZE;
 	return 0;
 }
diff --git a/arch/mips/mach-mscc/include/mach/ddr.h b/arch/mips/mach-mscc/include/mach/ddr.h
index d1f4287f65..bf75e52ec3 100644
--- a/arch/mips/mach-mscc/include/mach/ddr.h
+++ b/arch/mips/mach-mscc/include/mach/ddr.h
@@ -435,16 +435,12 @@ static inline void hal_vcoreiii_ddr_failed(void)
 	reset = KSEG0ADDR(_machine_restart);
 	icache_lock((void *)reset, 128);
 	asm volatile ("jr %0"::"r" (reset));
-
-	panic("DDR init failed\n");
 }
 #else				/* JR2 || ServalT */
 static inline void hal_vcoreiii_ddr_failed(void)
 {
 	writel(0, BASE_CFG + ICPU_RESET);
 	writel(PERF_SOFT_RST_SOFT_CHIP_RST, BASE_CFG + PERF_SOFT_RST);
-
-	panic("DDR init failed\n");
 }
 #endif
 
diff --git a/arch/mips/mach-mscc/lowlevel_init.S b/arch/mips/mach-mscc/lowlevel_init.S
index dfbe06766c..91f29ae252 100644
--- a/arch/mips/mach-mscc/lowlevel_init.S
+++ b/arch/mips/mach-mscc/lowlevel_init.S
@@ -8,6 +8,7 @@
 
     .set noreorder
     .extern     vcoreiii_tlb_init
+    .extern     vcoreiii_ddr_init
 #ifdef CONFIG_SOC_LUTON
     .extern     pll_init
 #endif
@@ -17,14 +18,28 @@ LEAF(lowlevel_init)
 	 * As we have no stack yet, we can assume the restricted
 	 * luxury of the sX-registers without saving them
 	 */
-	move	s0,ra
+
+	/* Modify ra/s0 such we return to physical NOR location */
+	li	t0, 0x0fffffff
+	li	t1, CONFIG_SYS_TEXT_BASE
+	and	s0, ra, t0
+	add	s0, s0, t1
 
 	jal	vcoreiii_tlb_init
 	 nop
+
 #ifdef CONFIG_SOC_LUTON
 	jal	pll_init
 	 nop
 #endif
+
+	/* Initialize DDR controller to enable stack/gd/heap */
+0:
+	jal	vcoreiii_ddr_init
+	 nop
+	bnez	v0, 0b		/* Retry on error */
+	 nop
+
 	jr	s0
 	 nop
 	END(lowlevel_init)
-- 
2.23.0