platform: generic: thead: fix stale TLB entries for th1520/sg2042

The TLB entries remain functional all the time once added in T-HEAD th1520
and Sophgo sg2042 (even if the MMU is then disabled afterwards). If there
are some stale TLB entries that contains the address of SBI, it will cause
unexpected memory access and issue a illegal instruction error. To avoid
this, a TLB flush is needed to drop these TLB entries before any memory
access in the trap handler.

To handle this workaroud, add a custom trap handler with executing TLB flush
first in the T-HEAD platform to fix affected socs.

Signed-off-by: Inochi Amaoto <inochiama@outlook.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

platform/generic/Kconfig

@@ -52,6 +52,10 @@ config PLATFORM_STARFIVE_JH7110
 	bool "StarFive JH7110 support"
 	default n
 
+config PLATFORM_THEAD
+	bool "THEAD C9xx support"
+	default n
+
 source "$(OPENSBI_SRC_DIR)/platform/generic/andes/Kconfig"
 
 endif

platform/generic/configs/defconfig

@@ -4,6 +4,7 @@ CONFIG_PLATFORM_RENESAS_RZFIVE=y
 CONFIG_PLATFORM_SIFIVE_FU540=y
 CONFIG_PLATFORM_SIFIVE_FU740=y
 CONFIG_PLATFORM_STARFIVE_JH7110=y
+CONFIG_PLATFORM_THEAD=y
 CONFIG_FDT_GPIO=y
 CONFIG_FDT_GPIO_DESIGNWARE=y
 CONFIG_FDT_GPIO_SIFIVE=y

platform/generic/thead/objects.mk

@@ -0,0 +1,10 @@
+#
+# SPDX-License-Identifier: BSD-2-Clause
+#
+# Copyright (C) 2023 Inochi Amaoto <inochiama@outlook.com>
+# Copyright (C) 2023 Alibaba Group Holding Limited.
+#
+
+carray-platform_override_modules-$(CONFIG_PLATFORM_THEAD) += thead_generic
+platform-objs-$(CONFIG_PLATFORM_THEAD) += thead/thead-generic.o
+platform-objs-$(CONFIG_PLATFORM_THEAD) += thead/thead-trap-handler.o

platform/generic/thead/thead-generic.c

@@ -0,0 +1,50 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Authors:
+ *   Inochi Amaoto <inochiama@outlook.com>
+ *
+ */
+
+#include <platform_override.h>
+#include <sbi/riscv_barrier.h>
+#include <sbi/sbi_const.h>
+#include <sbi/sbi_platform.h>
+#include <sbi/sbi_scratch.h>
+#include <sbi/sbi_string.h>
+#include <sbi_utils/fdt/fdt_helper.h>
+
+/**
+ * T-HEAD board with this quirk need to execute sfence.vma to flush
+ * stale entrie avoid incorrect memory access.
+ */
+#define THEAD_QUIRK_TLB_FLUSH_FIXUP		BIT(0)
+
+void _thead_tlb_flush_fixup_trap_handler(void);
+
+void thead_register_tlb_flush_trap_handler(void)
+{
+	csr_write(CSR_MTVEC, &_thead_tlb_flush_fixup_trap_handler);
+}
+
+static int thead_generic_early_init(bool cold_boot,
+				    const struct fdt_match *match)
+{
+	unsigned long quirks = (unsigned long)match->data;
+
+	if (quirks & THEAD_QUIRK_TLB_FLUSH_FIXUP)
+		thead_register_tlb_flush_trap_handler();
+
+	return 0;
+}
+
+static const struct fdt_match thead_generic_match[] = {
+	{ .compatible = "thead,th1520",
+	  .data = (void*)THEAD_QUIRK_TLB_FLUSH_FIXUP },
+	{ },
+};
+
+const struct platform_override thead_generic = {
+	.match_table	= thead_generic_match,
+	.early_init	= thead_generic_early_init,
+};

platform/generic/thead/thead-trap-handler.S

@@ -0,0 +1,13 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Authors:
+ *   Inochi Amaoto <inochiama@outlook.com>
+ *
+ */
+	.section .entry, "ax", %progbits
+	.align 3
+	.globl _thead_tlb_flush_fixup_trap_handler
+_thead_tlb_flush_fixup_trap_handler:
+	sfence.vma t0, zero
+	j _trap_handler