[PATCH] coresight: trbe: Add ISB after TRBLIMITR write

[Anshuman Khandual]

On 09/06/25 3:49 PM, James Clark wrote:
> DEN0154 states that hardware will be allowed to ignore writes to TRB*
> registers while the trace buffer is enabled. Add an ISB to ensure that
> it's disabled before clearing the other registers.
> 
> This is purely defensive because it's expected that arm_trbe_disable()
> would be called before teardown which has the required ISB.
> 
> Fixes: a2b579c41fe9 ("coresight: trbe: Remove redundant disable call")
> Signed-off-by: James Clark <james.clark at linaro.org>

Agreed. An isb() barrier is required to ensure that the TRBE is disabled
even after clearing TRBLIMITR_EL1 and before writing/clearing other TRBE
registers. Besides trbe_reset_local() seems to be the only function where
such a scenario exists.

LGTM.

Reviewed-by: Anshuman Khandual <anshuman.khandual at arm.com>

> ---
>  drivers/hwtracing/coresight/coresight-trbe.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> index 8267dd1a2130..10f3fb401edf 100644
> --- a/drivers/hwtracing/coresight/coresight-trbe.c
> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> @@ -257,6 +257,7 @@ static void trbe_drain_and_disable_local(struct trbe_cpudata *cpudata)
>  static void trbe_reset_local(struct trbe_cpudata *cpudata)
>  {
>  	write_sysreg_s(0, SYS_TRBLIMITR_EL1);
> +	isb();
>  	trbe_drain_buffer();
>  	write_sysreg_s(0, SYS_TRBPTR_EL1);
>  	write_sysreg_s(0, SYS_TRBBASER_EL1);
> 
> ---
> base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494
> change-id: 20250609-james-cs-trblimitr-isb-523f20d874d6
> 
> Best regards,