Re: [PATCH V2] clocksource: riscv: Patch riscv_clock_next_event() jump before first use

From: Palmer Dabbelt
Date: Thu Feb 09 2023 - 15:36:23 EST


On Wed, 01 Feb 2023 11:49:42 PST (-0800), Matt Evans wrote:
A static key is used to select between SBI and Sstc timer usage in
riscv_clock_next_event(), but currently the direction is resolved
after cpuhp_setup_state() is called (which sets the next event). The
first event will therefore fall through the sbi_set_timer() path; this
breaks Sstc-only systems. So, apply the jump patching before first
use.

Fixes: 9f7a8ff6391f ("RISC-V: Prefer sstc extension if available")
Signed-off-by: Matt Evans <mev@xxxxxxxxxxxx>
---

V1 -> V2: Commit msg tweak.

drivers/clocksource/timer-riscv.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
index 969a552da8d2..a36d173fd6cd 100644
--- a/drivers/clocksource/timer-riscv.c
+++ b/drivers/clocksource/timer-riscv.c
@@ -177,6 +177,11 @@ static int __init riscv_timer_init_dt(struct device_node *n)
return 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);
+ }
+
error = cpuhp_setup_state(CPUHP_AP_RISCV_TIMER_STARTING,
"clockevents/riscv/timer:starting",
riscv_timer_starting_cpu, riscv_timer_dying_cpu);
@@ -184,11 +189,6 @@ static int __init riscv_timer_init_dt(struct device_node *n)
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;
}
--
2.30.2

Reviewed-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>

Looks like I've taken stuff here before, but I'm also happy to have the clocksource folks pick this up so

Acked-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>

I don't think this is a particularly critical fix, as IIUC there's still no Sstc-only hardware in the real world. Given how late we are I'd err towards putting this on for-next anyway, so I'll give the clocksource folks a bit more time to chime in. Otherwise I'll put it on for-next before the merge window (assuming we're got an rc8 coming).

Thanks!