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 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.

-- 
Ville Syrjälä
Intel
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