Re: [RFC] drm/print: Introduce drm_line_printer

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

On Tue, 14 May 2024, Michal Wajdeczko <michal.wajdeczko@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.

Interesting. Nothing another level of abstraction can't solve. ;)

Except maybe it'll make adding function names to debug printers harder.

No strong feelings either way about it, I'll let others chime in.

A few comments inline.


BR,
Jani.

>
> Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
> ---
>  drivers/gpu/drm/drm_print.c |  9 +++++++++
>  include/drm/drm_print.h     | 37 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 46 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
> index cf2efb44722c..d6fb50d3407a 100644
> --- a/drivers/gpu/drm/drm_print.c
> +++ b/drivers/gpu/drm/drm_print.c
> @@ -214,6 +214,15 @@ 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 line = (uintptr_t)(++p->prefix);

Subtle. Might warrant adding a union in struct drm_printer for clarity.

> +	struct drm_printer *dp = p->arg;
> +
> +	drm_printf(dp, "%u: %pV", line, 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..58cc73c53853 100644
> --- a/include/drm/drm_print.h
> +++ b/include/drm/drm_print.h
> @@ -186,6 +186,7 @@ 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 +358,42 @@ 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
> + * @dp: the &struct drm_printer which actually generates 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.
> + *
> + * For example::
> + *
> + *	void crash_dump(struct drm_device *drm)
> + *	{
> + *		struct drm_printer dp = drm_err_printer(drm, "crash");
> + *		struct drm_printer lp = drm_line_printer(&dp);
> + *
> + *		drm_printf(&lp, "foo");
> + *		drm_printf(&lp, "bar");
> + *	}
> + *
> + * Above code will print into the dmesg something like::
> + *
> + *	[ ] 0000:00:00.0: [drm] *ERROR* crash 1: foo
> + *	[ ] 0000:00:00.0: [drm] *ERROR* crash 2: bar
> + *
> + * RETURNS:
> + * The &drm_printer object
> + */
> +static inline struct drm_printer drm_line_printer(struct drm_printer *dp)

Just p is customary for the drm_printer. "dp" gives me too much Display
Port vibes.

> +{
> +	struct drm_printer lp = {
> +		.printfn = __drm_printfn_line,
> +		.arg = dp,
> +	};
> +	return lp;
> +}
> +
>  /*
>   * struct device based logging
>   *

-- 
Jani Nikula, Intel