linux-kernel - Re: [PATCH] coresight: cpu-debug: control default behavior via Kconfig

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Date:   Mon, 6 Sep 2021 09:37:30 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Brian Norris <briannorris@...omium.org>
Cc:     Leo Yan <leo.yan@...aro.org>, Mike Leach <mike.leach@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        coresight@...ts.linaro.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] coresight: cpu-debug: control default behavior via
 Kconfig

Hi Brian,

On Fri, Sep 03, 2021 at 06:28:54PM -0700, Brian Norris wrote:
> Debugfs is nice and so are module parameters, but
>  * debugfs doesn't take effect early (e.g., if drivers are locking up
>    before user space gets anywhere)
>  * module parameters either add a lot to the kernel command line, or
>    else take effect late as well (if you build =m and configure in
>    /etc/modprobe.d/)
> 
> So in the same spirit as these
>   CONFIG_PANIC_ON_OOPS (also available via cmdline or modparam)
>   CONFIG_INTEL_IOMMU_DEFAULT_ON (also available via cmdline)
> add a new Kconfig option.
> 
> Module parameters and debugfs can still override.
> 
> Signed-off-by: Brian Norris <briannorris@...omium.org>
> ---
> 
>  drivers/hwtracing/coresight/Kconfig               | 13 +++++++++++++
>  drivers/hwtracing/coresight/coresight-cpu-debug.c |  2 +-
>  2 files changed, 14 insertions(+), 1 deletion(-)
> 

I have applied this patch to my local tree.  I will make that tree public when
next week when 5.15-rc1 has been released.

Thanks,
Mathieu

> diff --git a/drivers/hwtracing/coresight/Kconfig b/drivers/hwtracing/coresight/Kconfig
> index f026e5c0e777..8b638eb3cb7d 100644
> --- a/drivers/hwtracing/coresight/Kconfig
> +++ b/drivers/hwtracing/coresight/Kconfig
> @@ -150,6 +150,19 @@ config CORESIGHT_CPU_DEBUG
>  	  To compile this driver as a module, choose M here: the
>  	  module will be called coresight-cpu-debug.
>  
> +config CORESIGHT_CPU_DEBUG_DEFAULT_ON
> +	bool "Enable CoreSight CPU Debug by default
> +	depends on CORESIGHT_CPU_DEBUG
> +	help
> +	  Say Y here to enable the CoreSight Debug panic-debug by default. This
> +	  can also be enabled via debugfs, but this ensures the debug feature
> +	  is enabled as early as possible.
> +
> +	  Has the same effect as setting coresight_cpu_debug.enable=1 on the
> +	  kernel command line.
> +
> +	  Say N if unsure.
> +
>  config CORESIGHT_CTI
>  	tristate "CoreSight Cross Trigger Interface (CTI) driver"
>  	depends on ARM || ARM64
> diff --git a/drivers/hwtracing/coresight/coresight-cpu-debug.c b/drivers/hwtracing/coresight/coresight-cpu-debug.c
> index 00de46565bc4..8845ec4b4402 100644
> --- a/drivers/hwtracing/coresight/coresight-cpu-debug.c
> +++ b/drivers/hwtracing/coresight/coresight-cpu-debug.c
> @@ -105,7 +105,7 @@ static DEFINE_PER_CPU(struct debug_drvdata *, debug_drvdata);
>  static int debug_count;
>  static struct dentry *debug_debugfs_dir;
>  
> -static bool debug_enable;
> +static bool debug_enable = IS_ENABLED(CONFIG_CORESIGHT_CPU_DEBUG_DEFAULT_ON);
>  module_param_named(enable, debug_enable, bool, 0600);
>  MODULE_PARM_DESC(enable, "Control to enable coresight CPU debug functionality");
>  
> -- 
> 2.33.0.153.gba50c8fa24-goog
>