linux-kernel - Re: [PATCHv2 2/2] coresight: Abort probe if cpus are not available

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Date:   Fri, 21 Jun 2019 10:40:02 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     saiprakash.ranjan@...eaurora.org, mathieu.poirier@...aro.org,
        leo.yan@...aro.org, robh+dt@...nel.org, devicetree@...r.kernel.org,
        alexander.shishkin@...ux.intel.com, david.brown@...aro.org,
        mark.rutland@....com
Cc:     rnayak@...eaurora.org, vivek.gautam@...eaurora.org,
        sibis@...eaurora.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCHv2 2/2] coresight: Abort probe if cpus are not available

On 06/20/2019 07:31 PM, Sai Prakash Ranjan wrote:
> Currently coresight etm and cpu-debug will go ahead with
> the probe even when corresponding cpus are not available
> and error out later in the probe path. In such cases, it
> is better to abort the probe earlier.
> 
> Without this, setting *nosmp* will throw below errors:
> 
>   [    5.910622] coresight-cpu-debug 850000.debug: Coresight debug-CPU0 initialized
>   [    5.914266] coresight-cpu-debug 852000.debug: CPU1 debug arch init failed
>   [    5.921474] coresight-cpu-debug 854000.debug: CPU2 debug arch init failed
>   [    5.928328] coresight-cpu-debug 856000.debug: CPU3 debug arch init failed
>   [    5.935330] coresight etm0: CPU0: ETM v4.0 initialized
>   [    5.941875] coresight-etm4x 85d000.etm: ETM arch init failed
>   [    5.946794] coresight-etm4x: probe of 85d000.etm failed with error -22
>   [    5.952707] coresight-etm4x 85e000.etm: ETM arch init failed
>   [    5.958945] coresight-etm4x: probe of 85e000.etm failed with error -22
>   [    5.964853] coresight-etm4x 85f000.etm: ETM arch init failed
>   [    5.971096] coresight-etm4x: probe of 85f000.etm failed with error -22

That is expected. What else do you expect ?

> 
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
> ---
>   drivers/hwtracing/coresight/coresight-platform.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-platform.c b/drivers/hwtracing/coresight/coresight-platform.c
> index 8b03fa573684..3f4559596c6b 100644
> --- a/drivers/hwtracing/coresight/coresight-platform.c
> +++ b/drivers/hwtracing/coresight/coresight-platform.c
> @@ -168,6 +168,9 @@ static int of_coresight_get_cpu(struct device *dev)
>   	cpu = of_cpu_node_to_id(dn);
>   	of_node_put(dn);
>   
> +	if (num_online_cpus() <= cpu)
> +		return -ENODEV;

That is a pointless and terribly wrong check. What if you have only 2
online CPUs (CPU0 and CPU4) and you were processing the ETM for CPU4 ?

More over you should simply let the driver handle a case where the CPU
is not online. May be the driver could register a hotplug notifier and
bring itself up when the CPU comes online.

So, please drop this patch.

Kind regards
Suzuki