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SubjectRe: [PATCH] coresight: trbe: Move check for kernelspace unmapped at EL0 to probe
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On 2/1/22 5:52 PM, Sudeep Holla wrote:
> Currently with the check present in the module initialisation, it shouts
> on all the systems irrespective of presence of coresight trace buffer
> extensions.

IIUC a system with CONFIG_CORESIGHT_TRBE enabled but without a TRBE DT
i.e "arm,trace-buffer-extension" complains about kernel space unmapping
at EL0 (even though it does not even really have TRBE HW to initialize).

>
> Similar to Arm SPE perf driver, move the check for kernelspace unmapping
> when running at EL0 to the device probe instead of module initialisation.

Makes sense.

>
> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> Cc: Mike Leach <mike.leach@linaro.org>
> Cc: Leo Yan <leo.yan@linaro.org>
> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> Cc: coresight@lists.linaro.org
> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> ---
> drivers/hwtracing/coresight/coresight-trbe.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> index 276862c07e32..3fe2ce1ba5bf 100644
> --- a/drivers/hwtracing/coresight/coresight-trbe.c
> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> @@ -1423,6 +1423,11 @@ static int arm_trbe_device_probe(struct platform_device *pdev)
> struct device *dev = &pdev->dev;
> int ret;
>

Could you please add a similar comment like SPE driver regarding how
the TRBE buffer will be inaccessible, if kernel gets unmapped at EL0
and trace capture will terminate.

> + if (arm64_kernel_unmapped_at_el0()) {
> + pr_err("TRBE wouldn't work if kernel gets unmapped at EL0\n");
> + return -EOPNOTSUPP;
> + }
> +
> drvdata = devm_kzalloc(dev, sizeof(*drvdata), GFP_KERNEL);
> if (!drvdata)
> return -ENOMEM;
> @@ -1484,11 +1489,6 @@ static int __init arm_trbe_init(void)
> {
> int ret;
>
> - if (arm64_kernel_unmapped_at_el0()) {
> - pr_err("TRBE wouldn't work if kernel gets unmapped at EL0\n");
> - return -EOPNOTSUPP;
> - }
> -
> ret = platform_driver_register(&arm_trbe_driver);
> if (!ret)
> return 0;
>

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