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lib: timer: Provide a hart based timer feature

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As per the RISC-V specification, time value can be obtained from a time
CSR implemented in hardware or a MMIO based IP block. Qemu virt machine
already supports timer csr while CLINT provides the timer for other
platforms.

Implement a hart specific timer feature that can be detected at runtime.
As CSR based timer implementation are faster than MMIO address based, it
is always preferred over MMIO based one.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Tested-by: Jonathan Balkind <jbalkind@cs.princeton.edu>
Reviewed-by: Anup Patel <anup.patel@wdc.com>
This commit is contained in:
Atish Patra
2020-05-09 16:47:30 -07:00
committed by Anup Patel
parent 4938024420
commit ec0d2a7d7d
3 changed files with 28 additions and 9 deletions
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6
lib/sbi/sbi_hart.c
View File

@@ -271,6 +271,12 @@ static void sbi_hart_detect_features(u32 hartid)
feature |= SBI_HART_HAS_MCOUNTEREN;
}
/* Detect if hart supports time CSR */
trap.cause = 0;
csr_read_allowed(CSR_TIME, (unsigned long)&trap);
if (!trap.cause)
feature |= SBI_HART_HAS_TIME;
sbi_hart_set_feature(hartid, feature);
}

29
lib/sbi/sbi_timer.c
View File

@@ -10,14 +10,16 @@
#include <sbi/riscv_asm.h>
#include <sbi/riscv_encoding.h>
#include <sbi/sbi_error.h>
#include <sbi/sbi_hart.h>
#include <sbi/sbi_platform.h>
#include <sbi/sbi_scratch.h>
#include <sbi/sbi_timer.h>
static unsigned long time_delta_off;
static u64 (*get_time_val)(const struct sbi_platform *plat);
#if __riscv_xlen == 32
u64 get_ticks(void)
static u64 get_ticks(const struct sbi_platform *plat)
{
u32 lo, hi, tmp;
__asm__ __volatile__("1:\n"
@@ -29,7 +31,7 @@ u64 get_ticks(void)
return ((u64)hi << 32) | lo;
}
#else
u64 get_ticks(void)
static u64 get_ticks(const struct sbi_platform *plat)
{
unsigned long n;
@@ -40,12 +42,7 @@ u64 get_ticks(void)
u64 sbi_timer_value(void)
{
const struct sbi_platform *plat = sbi_platform_thishart_ptr();
if (sbi_platform_has_timer_value(plat))
return sbi_platform_timer_value(plat);
else
return get_ticks();
return get_time_val(sbi_platform_thishart_ptr());
}
u64 sbi_timer_virt_value(void)
@@ -97,6 +94,8 @@ void sbi_timer_process(void)
int sbi_timer_init(struct sbi_scratch *scratch, bool cold_boot)
{
u64 *time_delta;
const struct sbi_platform *plat = sbi_platform_ptr(scratch);
int ret;
if (cold_boot) {
time_delta_off = sbi_scratch_alloc_offset(sizeof(*time_delta),
@@ -111,7 +110,19 @@ int sbi_timer_init(struct sbi_scratch *scratch, bool cold_boot)
time_delta = sbi_scratch_offset_ptr(scratch, time_delta_off);
*time_delta = 0;
return sbi_platform_timer_init(sbi_platform_ptr(scratch), cold_boot);
ret = sbi_platform_timer_init(plat, cold_boot);
if (ret)
return ret;
if (sbi_hart_has_feature(current_hartid(), SBI_HART_HAS_TIME))
get_time_val = get_ticks;
else if (sbi_platform_has_timer_value(plat))
get_time_val = sbi_platform_timer_value;
else
/* There is no method to provide timer value */
return SBI_ENODEV;
return 0;
}
void sbi_timer_exit(struct sbi_scratch *scratch)