Re: [PATCH 1/3] drm/print: Add generic drm dev printk function

[Jani Nikula <jani.nikula@intel.com>]

On Fri, 17 May 2024, Michal Wajdeczko <michal.wajdeczko@intel.com> wrote:
> We already have some drm printk functions that need to duplicate
> a code to get a similar format of the final result, for example:
>
>   [ ] 0000:00:00.0: [drm:foo] bar
>   [ ] 0000:00:00.0: [drm] foo bar
>   [ ] 0000:00:00.0: [drm] *ERROR* foo
>
> Add a generic __drm_dev_vprintk() function that can format the
> final message like all other existing function do and allows us
> to keep the formatting code in one place.

Nice idea!

> Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
> Cc: Jani Nikula <jani.nikula@intel.com>
> ---
>  drivers/gpu/drm/drm_print.c | 49 ++++++++++++++++++++-----------------
>  include/drm/drm_print.h     |  3 +++
>  2 files changed, 30 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
> index cf2efb44722c..a2b60c8245a1 100644
> --- a/drivers/gpu/drm/drm_print.c
> +++ b/drivers/gpu/drm/drm_print.c
> @@ -187,19 +187,12 @@ void __drm_printfn_dbg(struct drm_printer *p, struct va_format *vaf)
>  	const struct drm_device *drm = p->arg;
>  	const struct device *dev = drm ? drm->dev : NULL;
>  	enum drm_debug_category category = p->category;
> -	const char *prefix = p->prefix ?: "";
> -	const char *prefix_pad = p->prefix ? " " : "";
>  
>  	if (!__drm_debug_enabled(category))
>  		return;
>  
>  	/* Note: __builtin_return_address(0) is useless here. */
> -	if (dev)
> -		dev_printk(KERN_DEBUG, dev, "[" DRM_NAME "]%s%s %pV",
> -			   prefix_pad, prefix, vaf);
> -	else
> -		printk(KERN_DEBUG "[" DRM_NAME "]%s%s %pV",
> -		       prefix_pad, prefix, vaf);
> +	__drm_dev_vprintk(dev, KERN_DEBUG, NULL, p->prefix, vaf);
>  }
>  EXPORT_SYMBOL(__drm_printfn_dbg);
>  
> @@ -277,6 +270,29 @@ void drm_print_bits(struct drm_printer *p, unsigned long value,
>  }
>  EXPORT_SYMBOL(drm_print_bits);
>  
> +void __drm_dev_vprintk(const struct device *dev, const char *level,
> +		       const void *origin, const char *prefix,
> +		       struct va_format *vaf)
> +{
> +	const char *prefix_pad = prefix ? " " : (prefix = "");

Too clever, please just keep it simple:

	const char *prefix_pad = prefix ? " " : "";

	if (!prefix)
		prefix = "";

> +
> +	if (dev)
> +		if (origin)
> +			dev_printk(level, dev, "[" DRM_NAME ":%ps]%s%s %pV",
> +				   origin, prefix_pad, prefix, vaf);
> +		else
> +			dev_printk(level, dev, "[" DRM_NAME "]%s%s %pV",
> +				   prefix_pad, prefix, vaf);
> +	else
> +		if (origin)
> +			printk("%s" "[" DRM_NAME ":%ps]%s%s %pV",
> +			       level, origin, prefix_pad, prefix, vaf);
> +		else
> +			printk("%s" "[" DRM_NAME "]%s%s %pV",
> +			       level, prefix_pad, prefix, vaf);

I'd sprinkle a few curly braces around the top level if-else blocks.

Side note, feels like using DRM_NAME makes things harder, not
easier. But that's for another patch.

> +}
> +EXPORT_SYMBOL(__drm_dev_vprintk);

AFAICT this could be a non-exported static function. And probably moved
earlier in the file to not require a declaration.

BR,
Jani.

> +
>  void drm_dev_printk(const struct device *dev, const char *level,
>  		    const char *format, ...)
>  {
> @@ -287,12 +303,7 @@ void drm_dev_printk(const struct device *dev, const char *level,
>  	vaf.fmt = format;
>  	vaf.va = &args;
>  
> -	if (dev)
> -		dev_printk(level, dev, "[" DRM_NAME ":%ps] %pV",
> -			   __builtin_return_address(0), &vaf);
> -	else
> -		printk("%s" "[" DRM_NAME ":%ps] %pV",
> -		       level, __builtin_return_address(0), &vaf);
> +	__drm_dev_vprintk(dev, level, __builtin_return_address(0), NULL, &vaf);
>  
>  	va_end(args);
>  }
> @@ -312,12 +323,7 @@ void __drm_dev_dbg(struct _ddebug *desc, const struct device *dev,
>  	vaf.fmt = format;
>  	vaf.va = &args;
>  
> -	if (dev)
> -		dev_printk(KERN_DEBUG, dev, "[" DRM_NAME ":%ps] %pV",
> -			   __builtin_return_address(0), &vaf);
> -	else
> -		printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
> -		       __builtin_return_address(0), &vaf);
> +	__drm_dev_vprintk(dev, KERN_DEBUG, __builtin_return_address(0), NULL, &vaf);
>  
>  	va_end(args);
>  }
> @@ -351,8 +357,7 @@ void __drm_err(const char *format, ...)
>  	vaf.fmt = format;
>  	vaf.va = &args;
>  
> -	printk(KERN_ERR "[" DRM_NAME ":%ps] *ERROR* %pV",
> -	       __builtin_return_address(0), &vaf);
> +	__drm_dev_vprintk(NULL, KERN_ERR, __builtin_return_address(0), "*ERROR*", &vaf);
>  
>  	va_end(args);
>  }
> diff --git a/include/drm/drm_print.h b/include/drm/drm_print.h
> index 089950ad8681..bb1801c58544 100644
> --- a/include/drm/drm_print.h
> +++ b/include/drm/drm_print.h
> @@ -366,6 +366,9 @@ static inline struct drm_printer drm_err_printer(struct drm_device *drm,
>  __printf(3, 4)
>  void drm_dev_printk(const struct device *dev, const char *level,
>  		    const char *format, ...);
> +void __drm_dev_vprintk(const struct device *dev, const char *level,
> +		       const void *origin, const char *prefix,
> +		       struct va_format *vaf);
>  struct _ddebug;
>  __printf(4, 5)
>  void __drm_dev_dbg(struct _ddebug *desc, const struct device *dev,

-- 
Jani Nikula, Intel