drm/i915/bios: use a flag for vbt hdmi level shift presence

Submitted by Jani Nikula on Nov. 5, 2019, 1:39 p.m.

Details

Message ID 20191105133900.19590-1-jani.nikula@intel.com
State New
Headers show
Series "drm/i915/bios: use a flag for vbt hdmi level shift presence" ( rev: 1 ) in Intel GFX

Not browsing as part of any series.

Commit Message

Jani Nikula Nov. 5, 2019, 1:39 p.m.
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(-)

Patch hide | download patch | download mbox

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;
+	}
 
 	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;

Comments

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
On Tue, 05 Nov 2019, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> 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;

I wanted to add the distinction between the default_entry being bogus
and the VBT being bogus.

BR,
Jani.

>
> 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
On Tue, Nov 05, 2019 at 03:59:57PM +0200, Jani Nikula wrote:
> On Tue, 05 Nov 2019, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> > 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;
> 
> I wanted to add the distinction between the default_entry being bogus
> and the VBT being bogus.

Any 'default>=n_entries' check is dead code anyway so we'd not
lose anything with the simpler code.
On Tue, Nov 05, 2019 at 05:21:06PM +0200, Ville Syrjälä wrote:
> On Tue, Nov 05, 2019 at 03:59:57PM +0200, Jani Nikula wrote:
> > On Tue, 05 Nov 2019, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> > > 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;
> > 
> > I wanted to add the distinction between the default_entry being bogus
> > and the VBT being bogus.
> 
> Any 'default>=n_entries' check is dead code anyway so we'd not
> lose anything with the simpler code.

Hmm. I guess we would lose the bad_vbt->default fallback.
But that really should be dead code as well, so not entirely
convinced such a belt+suspenders approach is warranted.