linux-kernel - Re: [PATCH 1/2] drm: Only #define DEBUG if CONFIG_DYNAMIC

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Date:   Thu, 6 Dec 2018 10:40:42 +0800
From:   "Zhang, Jerry(Junwei)" <Jerry.Zhang@....com>
To:     Michel Dänzer <michel@...nzer.net>,
        Christian Koenig <christian.koenig@....com>,
        Huang Rui <ray.huang@....com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>
CC:     <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] drm: Only #define DEBUG if CONFIG_DYNAMIC_DEBUG is
 disabled

On 12/6/18 12:56 AM, Michel Dänzer wrote:
> From: Michel Dänzer <michel.daenzer@....com>
>
> The following cases are possible for pr_debug():
>
> 1. CONFIG_DYNAMIC_DEBUG disabled
>     a) DEBUG not defined: pr_debug() translates to no_printk(...), i.e.
>        it never generates any output.
>     b) DEBUG defined: pr_debug() translates to printk(KERN_DEBUG ...),
>        i.e. it generates output which doesn't appear in dmesg by default,
>        can be enabled dynamically.
>
> 2. CONFIG_DYNAMIC_DEBUG enabled: pr_debug() translates to
>     dynamic_pr_debug()
>     a) DEBUG not defined: dynamic_pr_debug() generates no output by
>        default, can be enabled dynamically.
>     b) DEBUG defined: dynamic_pr_debug() generates output by default,
>        can be disabled dynamically.
>
> The intention for drm_debug_printer() is to generate output which
> doesn't appear in dmesg by default, but can be enabled dynamically, i.e.
> cases 1b) and 2a). However, defining DEBUG unconditionally gave us 2b)
> instead of 2a) with CONFIG_DYNAMIC_DEBUG enabled.
>
> Fixes: 79a5ad2fdb3c ("drm: Enable pr_debug() for drm_printer")
> Signed-off-by: Michel Dänzer <michel.daenzer@....com>
Reviewed-by: Junwei Zhang <Jerry.Zhang@....com>

> ---
>   drivers/gpu/drm/drm_print.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
> index 0e7fc3e7dfb4..ee56e4a1b343 100644
> --- a/drivers/gpu/drm/drm_print.c
> +++ b/drivers/gpu/drm/drm_print.c
> @@ -23,11 +23,13 @@
>    * Rob Clark <robdclark@...il.com>
>    */
>   
> -#define DEBUG /* for pr_debug() */
> -
>   #include <stdarg.h>
>   #include <linux/seq_file.h>
>   #include <drm/drmP.h>
> +
> +#ifndef CONFIG_DYNAMIC_DEBUG
> +#define DEBUG /* for pr_debug() */
> +#endif
>   #include <drm/drm_print.h>
>   
>   void __drm_puts_coredump(struct drm_printer *p, const char *str)