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riscv: isr.S: dedicate a register to &current_cpu

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Stop using &_kernel as this is not SMP friendly. Let's use s0 (after
preserving its content) to hold &current_cpu instead so it won't have
to be reloaded 	each time it is needed. This will be even more relevant
when SMP support is added.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
This commit is contained in:
Nicolas Pitre 2022-03-09 17:21:27 -05:00 • committed by Anas Nashif
commit 4f5374854e
3 changed files with 29 additions and 18 deletions
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43
arch/riscv/core/isr.S
View file

@ -135,6 +135,10 @@ SECTION_FUNC(exception.entry, __irq_wrapper)
addi sp, sp, -__z_arch_esf_t_SIZEOF
DO_CALLER_SAVED(sr) ;
/* Save s0 in the esf and load it with &_current_cpu. */
sr s0, __z_arch_esf_t_s0_OFFSET(sp)
la s0, _kernel + ___kernel_t_cpus_OFFSET
#ifdef CONFIG_USERSPACE
/*
* The scratch register now contains either the user mode stack
@ -280,16 +284,15 @@ do_irq_offload:
lr a1, __z_arch_esf_t_a0_OFFSET(sp)
lr a0, __z_arch_esf_t_a1_OFFSET(sp)
/* Increment _kernel.cpus[0].nested variable */
la t2, _kernel
lw t3, _kernel_offset_to_nested(t2)
/* Increment _current_cpu->nested */
lw t3, ___cpu_t_nested_OFFSET(s0)
addi t4, t3, 1
sw t4, _kernel_offset_to_nested(t2)
sw t4, ___cpu_t_nested_OFFSET(s0)
bnez t3, 1f
/* Switch to interrupt stack */
mv t0, sp
lr sp, _kernel_offset_to_irq_stack(t2)
lr sp, ___cpu_t_irq_stack_OFFSET(s0)
/* Save thread stack pointer on interrupt stack */
addi sp, sp, -16
@ -349,20 +352,19 @@ valid_syscall_id:
/* Disable IRQs again before leaving */
csrc mstatus, MSTATUS_IEN
j no_reschedule
j might_have_rescheduled
#endif /* CONFIG_USERSPACE */
is_interrupt:
/* Increment _kernel.cpus[0].nested variable */
la t2, _kernel
lw t3, _kernel_offset_to_nested(t2)
/* Increment _current_cpu->nested */
lw t3, ___cpu_t_nested_OFFSET(s0)
addi t4, t3, 1
sw t4, _kernel_offset_to_nested(t2)
sw t4, ___cpu_t_nested_OFFSET(s0)
bnez t3, on_irq_stack
/* Switch to interrupt stack */
mv t0, sp
lr sp, _kernel_offset_to_irq_stack(t2)
lr sp, ___cpu_t_irq_stack_OFFSET(s0)
/*
* Save thread stack pointer on interrupt stack
@ -406,11 +408,10 @@ on_irq_stack:
jalr ra, t1, 0
irq_done:
/* Decrement _kernel.cpus[0].nested variable */
la t1, _kernel
lw t2, _kernel_offset_to_nested(t1)
/* Decrement _current_cpu->nested */
lw t2, ___cpu_t_nested_OFFSET(s0)
addi t2, t2, -1
sw t2, _kernel_offset_to_nested(t1)
sw t2, ___cpu_t_nested_OFFSET(s0)
bnez t2, no_reschedule
/* nested count is back to 0: Return to thread stack */
@ -422,9 +423,8 @@ irq_done:
reschedule:
/* Get pointer to _kernel.current */
la t0, _kernel
lr a1, _kernel_offset_to_current(t0)
/* Get pointer to current thread on this CPU */
lr a1, ___cpu_t_current_OFFSET(s0)
/*
* Get next thread to schedule with z_get_next_switch_handle().
@ -447,6 +447,10 @@ reschedule:
call z_riscv_switch
z_riscv_thread_start:
might_have_rescheduled:
/* SMP note: reload s0 with &_current_cpu as it might have changed */
no_reschedule:
#ifdef CONFIG_RISCV_SOC_CONTEXT_SAVE
@ -503,6 +507,9 @@ no_fp: /* make sure this is reflected in the restored mstatus */
1:
#endif
/* Restore s0 (it is no longer ours) */
lr s0, __z_arch_esf_t_s0_OFFSET(sp)
/* Restore caller-saved registers from thread stack */
DO_CALLER_SAVED(lr)

2
arch/riscv/core/offsets/offsets.c
View file

@ -79,6 +79,8 @@ GEN_OFFSET_SYM(z_arch_esf_t, a7);
GEN_OFFSET_SYM(z_arch_esf_t, mepc);
GEN_OFFSET_SYM(z_arch_esf_t, mstatus);
GEN_OFFSET_SYM(z_arch_esf_t, s0);
#ifdef CONFIG_USERSPACE
GEN_OFFSET_SYM(z_arch_esf_t, sp);
#endif

2
include/arch/riscv/exp.h
View file

@ -72,6 +72,8 @@ struct __esf {
ulong_t mepc; /* machine exception program counter */
ulong_t mstatus; /* machine status register */
ulong_t s0; /* callee-saved s0 */
#ifdef CONFIG_USERSPACE
ulong_t sp; /* preserved (user or kernel) stack pointer */
#endif