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RISC-V: Prefer sstc extension if available 

RISC-V ISA has sstc extension which allows updating the next clock event
via a CSR (stimecmp) instead of an SBI call. This should happen dynamically
if sstc extension is available. Otherwise, it will fallback to SBI call
to maintain backward compatibility.

Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Reviewed-by: Guo Ren <guoren@kernel.org>
Link: https://lore.kernel.org/r/20220722165047.519994-4-atishp@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
This commit is contained in:
Atish Patra 2022-07-22 09:50:46 -07:00 committed by Palmer Dabbelt
parent 464b0187ff
commit 9f7a8ff639
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GPG Key ID: 2E1319F35FBB1889
1 changed files with 24 additions and 1 deletions
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25
drivers/clocksource/timer-riscv.c
View File

@ -7,6 +7,9 @@
* either be read from the "time" and "timeh" CSRs, and can use the SBI to
* setup events, or directly accessed using MMIO registers.
*/
#define pr_fmt(fmt) "riscv-timer: " fmt
#include <linux/clocksource.h>
#include <linux/clockchips.h>
#include <linux/cpu.h>
@ -20,14 +23,28 @@
#include <linux/of_irq.h>
#include <clocksource/timer-riscv.h>
#include <asm/smp.h>
#include <asm/hwcap.h>
#include <asm/sbi.h>
#include <asm/timex.h>
static DEFINE_STATIC_KEY_FALSE(riscv_sstc_available);
static int riscv_clock_next_event(unsigned long delta,
struct clock_event_device *ce)
{
u64 next_tval = get_cycles64() + delta;
csr_set(CSR_IE, IE_TIE);
sbi_set_timer(get_cycles64() + delta);
if (static_branch_likely(&riscv_sstc_available)) {
#if defined(CONFIG_32BIT)
csr_write(CSR_STIMECMP, next_tval & 0xFFFFFFFF);
csr_write(CSR_STIMECMPH, next_tval >> 32);
#else
csr_write(CSR_STIMECMP, next_tval);
#endif
} else
sbi_set_timer(next_tval);
return 0;
}
@ -165,6 +182,12 @@ static int __init riscv_timer_init_dt(struct device_node *n)
if (error)
pr_err("cpu hp setup state failed for RISCV timer [%d]\n",
error);
if (riscv_isa_extension_available(NULL, SSTC)) {
pr_info("Timer interrupt in S-mode is available via sstc extension\n");
static_branch_enable(&riscv_sstc_available);
}
return error;
}