Re: [PATCH] drm/i915/bios: use a flag for vbt hdmi level shift presence

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

On Tue, Nov 05, 2019 at 03:39:00PM +0200, Jani Nikula wrote:
> The pre-initialized magic value is a bit silly, switch to a flag
> instead. While at it, clean up the validity checks. No functional
> changes apart from the added checks.
> 
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_bios.c | 10 +---------
>  drivers/gpu/drm/i915/display/intel_ddi.c  | 19 +++++++++++--------
>  drivers/gpu/drm/i915/i915_drv.h           |  8 ++------
>  3 files changed, 14 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
> index a03f56b7b4ef..c19b234bebe6 100644
> --- a/drivers/gpu/drm/i915/display/intel_bios.c
> +++ b/drivers/gpu/drm/i915/display/intel_bios.c
> @@ -1509,6 +1509,7 @@ static void parse_ddi_port(struct drm_i915_private *dev_priv,
>  			      port_name(port),
>  			      hdmi_level_shift);
>  		info->hdmi_level_shift = hdmi_level_shift;
> +		info->hdmi_level_shift_set = true;
>  	}
>  
>  	if (bdb_version >= 204) {
> @@ -1692,8 +1693,6 @@ parse_general_definitions(struct drm_i915_private *dev_priv,
>  static void
>  init_vbt_defaults(struct drm_i915_private *dev_priv)
>  {
> -	enum port port;
> -
>  	dev_priv->vbt.crt_ddc_pin = GMBUS_PIN_VGADDC;
>  
>  	/* Default to having backlight */
> @@ -1721,13 +1720,6 @@ init_vbt_defaults(struct drm_i915_private *dev_priv)
>  	dev_priv->vbt.lvds_ssc_freq = intel_bios_ssc_frequency(dev_priv,
>  			!HAS_PCH_SPLIT(dev_priv));
>  	DRM_DEBUG_KMS("Set default to SSC at %d kHz\n", dev_priv->vbt.lvds_ssc_freq);
> -
> -	for_each_port(port) {
> -		struct ddi_vbt_port_info *info =
> -			&dev_priv->vbt.ddi_port_info[port];
> -
> -		info->hdmi_level_shift = HDMI_LEVEL_SHIFT_UNKNOWN;
> -	}
>  }
>  
>  /* Defaults to initialize only if there is no VBT. */
> diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c b/drivers/gpu/drm/i915/display/intel_ddi.c
> index c91521bcf06a..ec51f6971b16 100644
> --- a/drivers/gpu/drm/i915/display/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/display/intel_ddi.c
> @@ -888,11 +888,10 @@ icl_get_combo_buf_trans(struct drm_i915_private *dev_priv, int type, int rate,
>  
>  static int intel_ddi_hdmi_level(struct drm_i915_private *dev_priv, enum port port)
>  {
> +	struct ddi_vbt_port_info *port_info = &dev_priv->vbt.ddi_port_info[port];
>  	int n_entries, level, default_entry;
>  	enum phy phy = intel_port_to_phy(dev_priv, port);
>  
> -	level = dev_priv->vbt.ddi_port_info[port].hdmi_level_shift;
> -
>  	if (INTEL_GEN(dev_priv) >= 12) {
>  		if (intel_phy_is_combo(dev_priv, phy))
>  			icl_get_combo_buf_trans(dev_priv, INTEL_OUTPUT_HDMI,
> @@ -927,14 +926,18 @@ static int intel_ddi_hdmi_level(struct drm_i915_private *dev_priv, enum port por
>  		return 0;
>  	}
>  
> -	/* Choose a good default if VBT is badly populated */
> -	if (level == HDMI_LEVEL_SHIFT_UNKNOWN || level >= n_entries)
> -		level = default_entry;
> -
>  	if (WARN_ON_ONCE(n_entries == 0))
>  		return 0;
> -	if (WARN_ON_ONCE(level >= n_entries))
> -		level = n_entries - 1;
> +
> +	if (WARN_ON_ONCE(default_entry >= n_entries))
> +		default_entry = n_entries - 1;
> +
> +	if (port_info->hdmi_level_shift_set &&
> +	    !WARN_ON_ONCE(port_info->hdmi_level_shift >= n_entries)) {
> +		level = port_info->hdmi_level_shift;
> +	} else {
> +		level = default_entry;
> +	}

I'd probably simplify that to something like:

if (level_shift_set)
	level = level_shift;
else
	level = default;
if (WARN_ON_ONCE(level >= n_entries))
	level = n_entries - 1;

Either way:
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

>  
>  	return level;
>  }
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 7e0f67babe20..67bdfe6de3fa 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -627,13 +627,9 @@ struct ddi_vbt_port_info {
>  
>  	int max_tmds_clock;
>  
> -	/*
> -	 * This is an index in the HDMI/DVI DDI buffer translation table.
> -	 * The special value HDMI_LEVEL_SHIFT_UNKNOWN means the VBT didn't
> -	 * populate this field.
> -	 */
> -#define HDMI_LEVEL_SHIFT_UNKNOWN	0xff
> +	/* This is an index in the HDMI/DVI DDI buffer translation table. */
>  	u8 hdmi_level_shift;
> +	u8 hdmi_level_shift_set:1;
>  
>  	u8 supports_dvi:1;
>  	u8 supports_hdmi:1;
> -- 
> 2.20.1

-- 
Ville Syrjälä
Intel
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