[PATCH v2] drm/print: Introduce drm_line_printer

[Jani Nikula]

On Tue, 28 May 2024, Michal Wajdeczko <michal.wajdeczko at intel.com> wrote:
> This drm printer wrapper can be used to increase the robustness of
> the captured output generated by any other drm_printer to make sure
> we didn't lost any intermediate lines of the output by adding line
> numbers to each output line. Helpful for capturing some crash data.
>
> Signed-off-by: Michal Wajdeczko <michal.wajdeczko at intel.com>
> Cc: Jani Nikula <jani.nikula at intel.com>
> Cc: John Harrison <John.C.Harrison at Intel.com>

Reviewed-by: Jani Nikula <jani.nikula at intel.com>


> ---
> v2: don't abuse prefix, use union instead (Jani)
>     don't use 'dp' as name, prefer 'p' (Jani)
>     add support for unique series identifier (John)
> ---
>  drivers/gpu/drm/drm_print.c | 14 ++++++++
>  include/drm/drm_print.h     | 68 ++++++++++++++++++++++++++++++++++++-
>  2 files changed, 81 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
> index cf2efb44722c..be9cbebff5b3 100644
> --- a/drivers/gpu/drm/drm_print.c
> +++ b/drivers/gpu/drm/drm_print.c
> @@ -214,6 +214,20 @@ void __drm_printfn_err(struct drm_printer *p, struct va_format *vaf)
>  }
>  EXPORT_SYMBOL(__drm_printfn_err);
>  
> +void __drm_printfn_line(struct drm_printer *p, struct va_format *vaf)
> +{
> +	unsigned int counter = ++p->line.counter;
> +	const char *prefix = p->prefix ?: "";
> +	const char *pad = p->prefix ? " " : "";
> +
> +	if (p->line.series)
> +		drm_printf(p->arg, "%s%s%u.%u: %pV",
> +			   prefix, pad, p->line.series, counter, vaf);
> +	else
> +		drm_printf(p->arg, "%s%s%u: %pV", prefix, pad, counter, vaf);
> +}
> +EXPORT_SYMBOL(__drm_printfn_line);
> +
>  /**
>   * drm_puts - print a const string to a &drm_printer stream
>   * @p: the &drm printer
> diff --git a/include/drm/drm_print.h b/include/drm/drm_print.h
> index 089950ad8681..f4d9b98d7909 100644
> --- a/include/drm/drm_print.h
> +++ b/include/drm/drm_print.h
> @@ -176,7 +176,13 @@ struct drm_printer {
>  	void (*puts)(struct drm_printer *p, const char *str);
>  	void *arg;
>  	const char *prefix;
> -	enum drm_debug_category category;
> +	union {
> +		enum drm_debug_category category;
> +		struct {
> +			unsigned short series;
> +			unsigned short counter;
> +		} line;
> +	};
>  };
>  
>  void __drm_printfn_coredump(struct drm_printer *p, struct va_format *vaf);
> @@ -186,6 +192,7 @@ void __drm_puts_seq_file(struct drm_printer *p, const char *str);
>  void __drm_printfn_info(struct drm_printer *p, struct va_format *vaf);
>  void __drm_printfn_dbg(struct drm_printer *p, struct va_format *vaf);
>  void __drm_printfn_err(struct drm_printer *p, struct va_format *vaf);
> +void __drm_printfn_line(struct drm_printer *p, struct va_format *vaf);
>  
>  __printf(2, 3)
>  void drm_printf(struct drm_printer *p, const char *f, ...);
> @@ -357,6 +364,65 @@ static inline struct drm_printer drm_err_printer(struct drm_device *drm,
>  	return p;
>  }
>  
> +/**
> + * drm_line_printer - construct a &drm_printer that prefixes outputs with line numbers
> + * @p: the &struct drm_printer which actually generates the output
> + * @prefix: optional output prefix, or NULL for no prefix
> + * @series: optional unique series identifier, or 0 to omit identifier in the output
> + *
> + * This printer can be used to increase the robustness of the captured output
> + * to make sure we didn't lost any intermediate lines of the output. Helpful
> + * while capturing some crash data.
> + *
> + * Example 1::
> + *
> + *	void crash_dump(struct drm_device *drm)
> + *	{
> + *		static unsigned short id;
> + *		struct drm_printer p = drm_err_printer(drm, "crash");
> + *		struct drm_printer lp = drm_line_printer(&p, "dump", ++id);
> + *
> + *		drm_printf(&lp, "foo");
> + *		drm_printf(&lp, "bar");
> + *	}
> + *
> + * Above code will print into the dmesg something like::
> + *
> + *	[ ] 0000:00:00.0: [drm] *ERROR* crash dump 1.1: foo
> + *	[ ] 0000:00:00.0: [drm] *ERROR* crash dump 1.2: bar
> + *
> + * Example 2::
> + *
> + *	void line_dump(struct device *dev)
> + *	{
> + *		struct drm_printer p = drm_info_printer(dev);
> + *		struct drm_printer lp = drm_line_printer(&p, NULL, 0);
> + *
> + *		drm_printf(&lp, "foo");
> + *		drm_printf(&lp, "bar");
> + *	}
> + *
> + * Above code will print::
> + *
> + *	[ ] 0000:00:00.0: [drm] 1: foo
> + *	[ ] 0000:00:00.0: [drm] 2: bar
> + *
> + * RETURNS:
> + * The &drm_printer object
> + */
> +static inline struct drm_printer drm_line_printer(struct drm_printer *p,
> +						  const char *prefix,
> +						  unsigned short series)
> +{
> +	struct drm_printer lp = {
> +		.printfn = __drm_printfn_line,
> +		.arg = p,
> +		.prefix = prefix,
> +		.line = { .series = series, },
> +	};
> +	return lp;
> +}
> +
>  /*
>   * struct device based logging
>   *

-- 
Jani Nikula, Intel