[RFC PATCH v2 2/2] platform: generic: thead: fix stale TLB entries for th1520/sg2042

[Inochi Amaoto]

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 at outlook.com>
---
 platform/generic/Kconfig                    |  4 ++
 platform/generic/configs/defconfig          |  1 +
 platform/generic/thead/objects.mk           | 10 ++++
 platform/generic/thead/thead-generic.c      | 61 +++++++++++++++++++++
 platform/generic/thead/thead-trap-handler.S | 33 +++++++++++
 5 files changed, 109 insertions(+)
 create mode 100644 platform/generic/thead/objects.mk
 create mode 100644 platform/generic/thead/thead-generic.c
 create mode 100644 platform/generic/thead/thead-trap-handler.S

diff --git a/platform/generic/Kconfig b/platform/generic/Kconfig
index 72768ed..68dd58c 100644
--- a/platform/generic/Kconfig
+++ b/platform/generic/Kconfig
@@ -52,6 +52,10 @@ config PLATFORM_STARFIVE_JH7110
 	bool "StarFive JH7110 support"
 	default n
 
+config PLATFORM_THEAD_GENERIC
+	bool "THEAD C9xx generic platform support"
+	default n
+
 source "$(OPENSBI_SRC_DIR)/platform/generic/andes/Kconfig"
 
 endif
diff --git a/platform/generic/configs/defconfig b/platform/generic/configs/defconfig
index 634d410..26f0874 100644
--- a/platform/generic/configs/defconfig
+++ b/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_GENERIC=y
 CONFIG_FDT_GPIO=y
 CONFIG_FDT_GPIO_DESIGNWARE=y
 CONFIG_FDT_GPIO_SIFIVE=y
diff --git a/platform/generic/thead/objects.mk b/platform/generic/thead/objects.mk
new file mode 100644
index 0000000..cbbab18
--- /dev/null
+++ b/platform/generic/thead/objects.mk
@@ -0,0 +1,10 @@
+#
+# SPDX-License-Identifier: BSD-2-Clause
+#
+# Copyright (C) 2023 Inochi Amaoto <inochiama at outlook.com>
+# Copyright (C) 2023 Alibaba Group Holding Limited.
+#
+
+carray-platform_override_modules-$(CONFIG_PLATFORM_THEAD_GENERIC) += thead_generic
+platform-objs-$(CONFIG_PLATFORM_THEAD_GENERIC) += thead/thead-generic.o
+platform-objs-$(CONFIG_PLATFORM_THEAD_GENERIC) += thead/thead-trap-handler.o
diff --git a/platform/generic/thead/thead-generic.c b/platform/generic/thead/thead-generic.c
new file mode 100644
index 0000000..4cfddf0
--- /dev/null
+++ b/platform/generic/thead/thead-generic.c
@@ -0,0 +1,61 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Authors:
+ *   Inochi Amaoto <inochiama at 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>
+
+#define THEAD_QUIRK_SFENCE_FIXUP		BIT(0)
+
+#define thead_get_symbol_local_address(_name)				\
+	({								\
+		register unsigned long __v;				\
+		__asm__ __volatile__ ("lla %0, " STRINGIFY(_name)	\
+				     : "=r"(__v)			\
+				     :					\
+				     : "memory");			\
+		(void*)__v;						\
+	})
+
+void thead_register_sfence_trap_handler(void)
+{
+	struct sbi_scratch *scratch = sbi_scratch_thishart_ptr();
+	void* trap_hanlder_addr = thead_get_symbol_local_address(
+						_thead_sfence_trap_handler);
+	void* trap_exit_addr = thead_get_symbol_local_address(
+						_thead_sfence_trap_exit);
+
+	csr_write(CSR_MTVEC, trap_hanlder_addr);
+	scratch->trap_exit = (unsigned long)trap_exit_addr;
+}
+
+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_SFENCE_FIXUP)
+		thead_register_sfence_trap_handler();
+
+	return 0;
+}
+
+static const struct fdt_match thead_generic_match[] = {
+	{ .compatible = "thead,th1520",
+	  .data = (void*)THEAD_QUIRK_SFENCE_FIXUP },
+	{ },
+};
+
+const struct platform_override thead_generic = {
+	.match_table	= thead_generic_match,
+	.early_init	= thead_generic_early_init,
+};
diff --git a/platform/generic/thead/thead-trap-handler.S b/platform/generic/thead/thead-trap-handler.S
new file mode 100644
index 0000000..ca27ea1
--- /dev/null
+++ b/platform/generic/thead/thead-trap-handler.S
@@ -0,0 +1,33 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Authors:
+ *   Inochi Amaoto <inochiama at outlook.com>
+ *
+ */
+
+#include <sbi/riscv_elf.h>
+#include <sbi/sbi_trap.h>
+
+	.section .entry, "ax", %progbits
+	.align 3
+	.globl _thead_sfence_trap_handler
+	.globl _thead_sfence_trap_exit
+_thead_sfence_trap_handler:
+	sfence.vma t0, zero
+
+	TRAP_SAVE_AND_SETUP_SP_T0
+
+	TRAP_SAVE_MEPC_MSTATUS 0
+
+	TRAP_SAVE_GENERAL_REGS_EXCEPT_SP_T0
+
+	TRAP_CALL_C_ROUTINE
+_thead_sfence_trap_exit:
+	TRAP_RESTORE_GENERAL_REGS_EXCEPT_A0_T0
+
+	TRAP_RESTORE_MEPC_MSTATUS 0
+
+	TRAP_RESTORE_A0_T0
+
+	mret
-- 
2.42.0