riscv: Add kconfig option to run U-Boot in S-mode
This patch adds kconfig option RISCV_SMODE to run U-Boot in
S-mode. When this opition is enabled we use s<xyz> CSRs instead
of m<xyz> CSRs.
It is important to note that there is no equivalent S-mode CSR
for misa and mhartid CSRs so we expect M-mode runtime firmware
(BBL or equivalent) to emulate misa and mhartid CSR read.
In-future, we will have more patches to avoid accessing misa and
mhartid CSRs from S-mode.
Signed-off-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 3e0af55..732a357 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -55,6 +55,11 @@
config RISCV_ISA_A
def_bool y
+config RISCV_SMODE
+ bool "Run in S-Mode"
+ help
+ Enable this option to build U-Boot for RISC-V S-Mode
+
config 32BIT
bool
diff --git a/arch/riscv/cpu/start.S b/arch/riscv/cpu/start.S
index 15e1b81..3f055bd 100644
--- a/arch/riscv/cpu/start.S
+++ b/arch/riscv/cpu/start.S
@@ -41,10 +41,10 @@
li t0, CONFIG_SYS_SDRAM_BASE
SREG a2, 0(t0)
la t0, trap_entry
- csrw mtvec, t0
+ csrw MODE_PREFIX(tvec), t0
/* mask all interrupts */
- csrw mie, zero
+ csrw MODE_PREFIX(ie), zero
/* Enable cache */
jal icache_enable
@@ -166,7 +166,7 @@
*/
la t0, trap_entry
add t0, t0, t6
- csrw mtvec, t0
+ csrw MODE_PREFIX(tvec), t0
clear_bss:
la t0, __bss_start /* t0 <- rel __bss_start in FLASH */
@@ -238,17 +238,24 @@
SREG x29, 29*REGBYTES(sp)
SREG x30, 30*REGBYTES(sp)
SREG x31, 31*REGBYTES(sp)
- csrr a0, mcause
- csrr a1, mepc
+ csrr a0, MODE_PREFIX(cause)
+ csrr a1, MODE_PREFIX(epc)
mv a2, sp
jal handle_trap
- csrw mepc, a0
+ csrw MODE_PREFIX(epc), a0
+#ifdef CONFIG_RISCV_SMODE
+/*
+ * Remain in S-mode after sret
+ */
+ li t0, SSTATUS_SPP
+#else
/*
* Remain in M-mode after mret
*/
li t0, MSTATUS_MPP
- csrs mstatus, t0
+#endif
+ csrs MODE_PREFIX(status), t0
LREG x1, 1*REGBYTES(sp)
LREG x2, 2*REGBYTES(sp)
LREG x3, 3*REGBYTES(sp)
@@ -281,4 +288,4 @@
LREG x30, 30*REGBYTES(sp)
LREG x31, 31*REGBYTES(sp)
addi sp, sp, 32*REGBYTES
- mret
+ MODE_PREFIX(ret)
diff --git a/arch/riscv/include/asm/encoding.h b/arch/riscv/include/asm/encoding.h
index 9ea50ce..97cf906 100644
--- a/arch/riscv/include/asm/encoding.h
+++ b/arch/riscv/include/asm/encoding.h
@@ -7,6 +7,12 @@
#ifndef RISCV_CSR_ENCODING_H
#define RISCV_CSR_ENCODING_H
+#ifdef CONFIG_RISCV_SMODE
+#define MODE_PREFIX(__suffix) s##__suffix
+#else
+#define MODE_PREFIX(__suffix) m##__suffix
+#endif
+
#define MSTATUS_UIE 0x00000001
#define MSTATUS_SIE 0x00000002
#define MSTATUS_HIE 0x00000004
diff --git a/arch/riscv/lib/interrupts.c b/arch/riscv/lib/interrupts.c
index 903a1c4..3aff006 100644
--- a/arch/riscv/lib/interrupts.c
+++ b/arch/riscv/lib/interrupts.c
@@ -34,17 +34,30 @@
return 0;
}
-ulong handle_trap(ulong mcause, ulong epc, struct pt_regs *regs)
+ulong handle_trap(ulong cause, ulong epc, struct pt_regs *regs)
{
- ulong is_int;
+ ulong is_irq, irq;
+
+ is_irq = (cause & MCAUSE_INT);
+ irq = (cause & ~MCAUSE_INT);
- is_int = (mcause & MCAUSE_INT);
- if ((is_int) && ((mcause & MCAUSE_CAUSE) == IRQ_M_EXT))
- external_interrupt(0); /* handle_m_ext_interrupt */
- else if ((is_int) && ((mcause & MCAUSE_CAUSE) == IRQ_M_TIMER))
- timer_interrupt(0); /* handle_m_timer_interrupt */
- else
- _exit_trap(mcause, epc, regs);
+ if (is_irq) {
+ switch (irq) {
+ case IRQ_M_EXT:
+ case IRQ_S_EXT:
+ external_interrupt(0); /* handle external interrupt */
+ break;
+ case IRQ_M_TIMER:
+ case IRQ_S_TIMER:
+ timer_interrupt(0); /* handle timer interrupt */
+ break;
+ default:
+ _exit_trap(cause, epc, regs);
+ break;
+ };
+ } else {
+ _exit_trap(cause, epc, regs);
+ }
return epc;
}