linux-kernel - Re: [PATCH V3 02/14] coresight: Do not scan for graph if none is present

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Date:   Tue, 2 Feb 2021 11:10:01 +0000
From:   Mike Leach <mike.leach@...aro.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Coresight ML <coresight@...ts.linaro.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        "Suzuki K. Poulose" <suzuki.poulose@....com>,
        Linu Cherian <lcherian@...vell.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 02/14] coresight: Do not scan for graph if none is present

Hi Ansuman,

On Wed, 27 Jan 2021 at 08:55, Anshuman Khandual
<anshuman.khandual@....com> wrote:
>
> From: Suzuki K Poulose <suzuki.poulose@....com>
>
> If a graph node is not found for a given node, of_get_next_endpoint()
> will emit the following error message :
>
>  OF: graph: no port node found in /<node_name>
>
> If the given component doesn't have any explicit connections (e.g,
> ETE) we could simply ignore the graph parsing.
>
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Mike Leach <mike.leach@...aro.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>  drivers/hwtracing/coresight/coresight-platform.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/drivers/hwtracing/coresight/coresight-platform.c b/drivers/hwtracing/coresight/coresight-platform.c
> index 3629b78..c594f45 100644
> --- a/drivers/hwtracing/coresight/coresight-platform.c
> +++ b/drivers/hwtracing/coresight/coresight-platform.c
> @@ -90,6 +90,12 @@ static void of_coresight_get_ports_legacy(const struct device_node *node,
>         struct of_endpoint endpoint;
>         int in = 0, out = 0;
>
> +       /*
> +        * Avoid warnings in of_graph_get_next_endpoint()
> +        * if the device doesn't have any graph connections
> +        */
> +       if (!of_graph_is_present(node))
> +         return;

The problem here is that you are masking genuine errors.
The solution is to either call this only if the device type is one
that ports are not required - i.e. ETE, or upgrade the .dts bindings
for the rest of the ETM devices to yaml so that the ports requirement
is checked and validated there.

Regards

Mike

>         do {
>                 ep = of_graph_get_next_endpoint(node, ep);
>                 if (!ep)
> --
> 2.7.4
>


-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK