[PATCH 3/4] perf/arm_cspmu: Improve sub-module error reporting

[Ilkka Koskinen]

On Thu, 9 Jul 2026, Robin Murphy wrote:

> When waiting for a sub-module to register, we return a bare
> -EPROBE_DEFER that ends up showing the end user:
>
>  platform arm-cs-arch-pmu.1: deferred probe pending (no reason)
>
> wherein it's not necessarily clear that they might need to take some
> action to ensure the appropriate module is available to load. Let's use
> dev_err_probe() here so we can show exactly what we're waiting for.
>
> Similarly, in the case where something's gone horribly wrong with an
> already-registered module, we can use dev_WARN() to standardise the
> device/driver attribution rather than just open-coding "arm_cspmu".
>
> Signed-off-by: Robin Murphy <robin.murphy at arm.com>

Looks good to me,

Reviewed-by: Ilkka Koskinen <ilkka at os.amperecomputing.com>

Cheers, Ilkka

> ---
> drivers/perf/arm_cspmu/arm_cspmu.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/perf/arm_cspmu/arm_cspmu.c b/drivers/perf/arm_cspmu/arm_cspmu.c
> index 0570be74d11f..0b26a1588eba 100644
> --- a/drivers/perf/arm_cspmu/arm_cspmu.c
> +++ b/drivers/perf/arm_cspmu/arm_cspmu.c
> @@ -438,13 +438,15 @@ static int arm_cspmu_init_impl_ops(struct arm_cspmu *cspmu)
> 				if (ret)
> 					module_put(match->module);
> 			} else {
> -				WARN(1, "arm_cspmu failed to get module: %s\n",
> +				dev_WARN(cspmu->dev, "Failed to get module: %s\n",
> 					match->module_name);
> 				ret = -EINVAL;
> 			}
> 		} else {
> 			request_module_nowait(match->module_name);
> -			ret = -EPROBE_DEFER;
> +			ret = dev_err_probe(cspmu->dev, -EPROBE_DEFER,
> +					    "Waiting for module %s to load\n",
> +					    match->module_name);
> 		}
>
> 		mutex_unlock(&arm_cspmu_lock);
> -- 
> 2.54.0.dirty
>
>