linux-kernel - Re: [PATCH] driver core: Don't require dynamic_debug for initcall

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Date:   Wed, 12 Apr 2023 16:02:16 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Stephen Boyd <swboyd@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Brian Norris <briannorris@...omium.org>
Subject: Re: [PATCH] driver core: Don't require dynamic_debug for
 initcall_debug probe timing



On 4/12/23 15:58, Stephen Boyd wrote:
> Don't require the use of dynamic debug (or modification of the kernel to
> add a #define DEBUG to the top of this file) to get the printk message
> about driver probe timing. This printk is only emitted when
> initcall_debug is enabled on the kernel commandline, and it isn't
> immediately obvious that you have to do something else to debug boot
> timing issues related to driver probe. Add a comment too so it doesn't
> get converted back to pr_debug().
> 
> Fixes: eb7fbc9fb118 ("driver core: Add missing '\n' in log messages")
> Cc: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> Cc: Brian Norris <briannorris@...omium.org>
> Signed-off-by: Stephen Boyd <swboyd@...omium.org>

Good one. Thanks for catching this.

Acked-by: Randy Dunlap <rdunlap@...radead.org>


> ---
>  drivers/base/dd.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 8def2ba08a82..1b16e0fb7658 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -708,7 +708,12 @@ static int really_probe_debug(struct device *dev, struct device_driver *drv)
>  	calltime = ktime_get();
>  	ret = really_probe(dev, drv);
>  	rettime = ktime_get();
> -	pr_debug("probe of %s returned %d after %lld usecs\n",
> +	/*
> +	 * Don't change this to pr_debug() because that requires
> +	 * CONFIG_DYNAMIC_DEBUG and we want a simple 'initcall_debug' on the
> +	 * kernel commandline to print this all the time at the debug level.
> +	 */
> +	printk(KERN_DEBUG "probe of %s returned %d after %lld usecs\n",
>  		 dev_name(dev), ret, ktime_us_delta(rettime, calltime));
>  	return ret;
>  }
> 
> base-commit: fe15c26ee26efa11741a7b632e9f23b01aca4cc6

-- 
~Randy