diff options
Diffstat (limited to 'arch/riscv/cpu/start.S')
| -rw-r--r-- | arch/riscv/cpu/start.S | 58 |
1 files changed, 45 insertions, 13 deletions
diff --git a/arch/riscv/cpu/start.S b/arch/riscv/cpu/start.S index bf9fdf369b4..bbc737ed9a2 100644 --- a/arch/riscv/cpu/start.S +++ b/arch/riscv/cpu/start.S @@ -43,14 +43,32 @@ _start: csrr a0, CSR_MHARTID #endif - /* save hart id and dtb pointer */ + /* + * Save hart id and dtb pointer. The thread pointer register is not + * modified by C code. It is used by secondary_hart_loop. + */ mv tp, a0 mv s1, a1 + /* + * Set the global data pointer to a known value in case we get a very + * early trap. The global data pointer will be set its actual value only + * after it has been initialized. + */ + mv gp, zero + + /* + * Set the trap handler. This must happen after initializing gp because + * the handler may use it. + */ la t0, trap_entry csrw MODE_PREFIX(tvec), t0 - /* mask all interrupts */ + /* + * Mask all interrupts. Interrupts are disabled globally (in m/sstatus) + * for U-Boot, but we will need to read m/sip to determine if we get an + * IPI + */ csrw MODE_PREFIX(ie), zero #if CONFIG_IS_ENABLED(SMP) @@ -65,8 +83,6 @@ _start: #else li t0, SIE_SSIE #endif - /* Clear any pending IPIs */ - csrc MODE_PREFIX(ip), t0 csrs MODE_PREFIX(ie), t0 #endif @@ -87,10 +103,10 @@ call_board_init_f_0: jal board_init_f_alloc_reserve /* - * Set global data pointer here for all harts, uninitialized at this - * point. + * Save global data pointer for later. We don't set it here because it + * is not initialized yet. */ - mv gp, a0 + mv s0, a0 /* setup stack */ #if CONFIG_IS_ENABLED(SMP) @@ -111,6 +127,14 @@ call_board_init_f_0: amoswap.w s2, t1, 0(t0) bnez s2, wait_for_gd_init #else + /* + * FIXME: gp is set before it is initialized. If an XIP U-Boot ever + * encounters a pending IPI on boot it is liable to jump to whatever + * memory happens to be in ipi_data.addr on boot. It may also run into + * problems if it encounters an exception too early (because printf/puts + * accesses gd). + */ + mv gp, s0 bnez tp, secondary_hart_loop #endif @@ -127,16 +151,21 @@ call_board_init_f_0: #ifndef CONFIG_XIP la t0, available_harts_lock - fence rw, w - amoswap.w zero, zero, 0(t0) + amoswap.w.rl zero, zero, 0(t0) wait_for_gd_init: la t0, available_harts_lock li t1, 1 -1: amoswap.w t1, t1, 0(t0) - fence r, rw +1: amoswap.w.aq t1, t1, 0(t0) bnez t1, 1b + /* + * Set the global data pointer only when gd_t has been initialized. + * This was already set by arch_setup_gd on the boot hart, but all other + * harts' global data pointers gets set here. + */ + mv gp, s0 + /* register available harts in the available_harts mask */ li t1, 1 sll t1, t1, tp @@ -144,8 +173,7 @@ wait_for_gd_init: or t2, t2, t1 SREG t2, GD_AVAILABLE_HARTS(gp) - fence rw, w - amoswap.w zero, zero, 0(t0) + amoswap.w.rl zero, zero, 0(t0) /* * Continue on hart lottery winner, others branch to @@ -395,6 +423,10 @@ secondary_hart_relocate: mv gp, a2 #endif +/* + * Interrupts are disabled globally, but they can still be read from m/sip. The + * wfi function will wake us up if we get an IPI, even if we do not trap. + */ secondary_hart_loop: wfi |