Re: [Intel-gfx] [PATCH 2/9] drm/edid: pass a timing pointer to is_display_descriptor()

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Mar 25, 2022 at 02:25:24PM +0200, Jani Nikula wrote:
> Use struct member access instead of direct offsets to avoid lots of
> casts all over the place.
> 
> Use BUILD_BUG_ON() for sanity check.
> 
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>  drivers/gpu/drm/drm_edid.c | 26 +++++++++++++++-----------
>  1 file changed, 15 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 1b552fe54f38..48707eef1dc2 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -2331,10 +2331,14 @@ struct drm_display_mode *drm_mode_find_dmt(struct drm_device *dev,
>  }
>  EXPORT_SYMBOL(drm_mode_find_dmt);
>  
> -static bool is_display_descriptor(const u8 d[18], u8 tag)
> +static bool is_display_descriptor(const struct detailed_timing *timing, u8 type)
>  {
> -	return d[0] == 0x00 && d[1] == 0x00 &&
> -		d[2] == 0x00 && d[3] == tag;
> +	BUILD_BUG_ON(offsetof(typeof(*timing), pixel_clock) != 0);
> +	BUILD_BUG_ON(offsetof(typeof(*timing), data.other_data.pad1) != 2);
> +	BUILD_BUG_ON(offsetof(typeof(*timing), data.other_data.type) != 3);
> +
> +	return timing->pixel_clock == 0 && timing->data.other_data.pad1 == 0 &&

This would probably be less confusing if we moved pixel_clock into
pixel_data and just had matching padding bytes/etc. in other_data.

The names of all structs are also rather weird. We should probably
change them to match the spec terminology a bit more closely:
18 byte descriptor,detailed timing descriptor,display descriptor.
But that's a separate topic.

> +		timing->data.other_data.type == type;
>  }
>  
>  static bool is_detailed_timing_descriptor(const u8 d[18])
> @@ -2405,7 +2409,7 @@ is_rb(struct detailed_timing *t, void *data)
>  {
>  	u8 *r = (u8 *)t;
>  
> -	if (!is_display_descriptor(r, EDID_DETAIL_MONITOR_RANGE))
> +	if (!is_display_descriptor(t, EDID_DETAIL_MONITOR_RANGE))
>  		return;
>  
>  	if (r[15] & 0x10)
> @@ -2431,7 +2435,7 @@ find_gtf2(struct detailed_timing *t, void *data)
>  {
>  	u8 *r = (u8 *)t;
>  
> -	if (!is_display_descriptor(r, EDID_DETAIL_MONITOR_RANGE))
> +	if (!is_display_descriptor(t, EDID_DETAIL_MONITOR_RANGE))
>  		return;
>  
>  	if (r[10] == 0x02)
> @@ -2987,7 +2991,7 @@ do_inferred_modes(struct detailed_timing *timing, void *c)
>  	struct detailed_non_pixel *data = &timing->data.other_data;
>  	struct detailed_data_monitor_range *range = &data->data.range;
>  
> -	if (!is_display_descriptor((const u8 *)timing, EDID_DETAIL_MONITOR_RANGE))
> +	if (!is_display_descriptor(timing, EDID_DETAIL_MONITOR_RANGE))
>  		return;
>  
>  	closure->modes += drm_dmt_modes_for_range(closure->connector,
> @@ -3067,7 +3071,7 @@ do_established_modes(struct detailed_timing *timing, void *c)
>  {
>  	struct detailed_mode_closure *closure = c;
>  
> -	if (!is_display_descriptor((const u8 *)timing, EDID_DETAIL_EST_TIMINGS))
> +	if (!is_display_descriptor(timing, EDID_DETAIL_EST_TIMINGS))
>  		return;
>  
>  	closure->modes += drm_est3_modes(closure->connector, timing);
> @@ -3122,7 +3126,7 @@ do_standard_modes(struct detailed_timing *timing, void *c)
>  	struct edid *edid = closure->edid;
>  	int i;
>  
> -	if (!is_display_descriptor((const u8 *)timing, EDID_DETAIL_STD_MODES))
> +	if (!is_display_descriptor(timing, EDID_DETAIL_STD_MODES))
>  		return;
>  
>  	for (i = 0; i < 6; i++) {
> @@ -3231,7 +3235,7 @@ do_cvt_mode(struct detailed_timing *timing, void *c)
>  {
>  	struct detailed_mode_closure *closure = c;
>  
> -	if (!is_display_descriptor((const u8 *)timing, EDID_DETAIL_CVT_3BYTE))
> +	if (!is_display_descriptor(timing, EDID_DETAIL_CVT_3BYTE))
>  		return;
>  
>  	closure->modes += drm_cvt_modes(closure->connector, timing);
> @@ -4491,7 +4495,7 @@ drm_parse_hdmi_vsdb_audio(struct drm_connector *connector, const u8 *db)
>  static void
>  monitor_name(struct detailed_timing *t, void *data)
>  {
> -	if (!is_display_descriptor((const u8 *)t, EDID_DETAIL_MONITOR_NAME))
> +	if (!is_display_descriptor(t, EDID_DETAIL_MONITOR_NAME))
>  		return;
>  
>  	*(u8 **)data = t->data.other_data.data.str.str;
> @@ -5226,7 +5230,7 @@ void get_monitor_range(struct detailed_timing *timing,
>  	const struct detailed_non_pixel *data = &timing->data.other_data;
>  	const struct detailed_data_monitor_range *range = &data->data.range;
>  
> -	if (!is_display_descriptor((const u8 *)timing, EDID_DETAIL_MONITOR_RANGE))
> +	if (!is_display_descriptor(timing, EDID_DETAIL_MONITOR_RANGE))
>  		return;
>  
>  	/*
> -- 
> 2.30.2

-- 
Ville Syrjälä
Intel