On Thu, May 01, 2025 at 11:54:58AM +0100, James Clark wrote:
On 01/05/2025 11:42 am, Leo Yan wrote:
The claim register is set twice in the restore flow; remove the duplicate operation.
Signed-off-by: Leo Yan leo.yan@arm.com
drivers/hwtracing/coresight/coresight-etm4x-core.c | 2 -- 1 file changed, 2 deletions(-)
diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c index 5c20ed4cf4ed..228317991ec2 100644 --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c @@ -1958,8 +1958,6 @@ static void __etm4_cpu_restore(struct etmv4_drvdata *drvdata) if (drvdata->numvmidc > 4) etm4x_relaxed_write32(csa, state->trcvmidcctlr0, TRCVMIDCCTLR1);
- etm4x_relaxed_write32(csa, state->trcclaimset, TRCCLAIMSET);
- if (!drvdata->skip_power_up) etm4x_relaxed_write32(csa, state->trcpdcr, TRCPDCR);
Reviewed-by: James Clark james.clark@linaro.org
Semi-related to this patch but probably not worth fixing: There's technically a race condition with an external debugger here. It would be better to use coresight_claim_device_unlocked() and report the error that's returned instead of manually writing to the whole claim register without checking it before and after like the claim function does.
I thought again and conclude the current patch would be fine (at least not bad ;)
The reason is the ETM driver has acquired the OS lock during idle states, this prevents the race condition with external debuggers.
And if a CPU detects pending interrupts and abort a low power flow, the CoreSight self claim tag is still set. In this case, coresight_claim_device_unlocked() will report unnecessary warnings.
Thanks, Leo