Re: [PATCH 09/10] drm/i915: Unify error handling for missing DDI buf trans tables

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

On Wed, Oct 18, 2017 at 08:52:40PM +0300, Ville Syrjälä wrote:
> On Wed, Oct 18, 2017 at 10:41:44AM -0700, James Ausmus wrote:
> > On Mon, Oct 16, 2017 at 05:57:04PM +0300, Ville Syrjala wrote:
> > > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > 
> > > Handle missing buf trans tables, or out of bounds buf trans levels
> > > the same way everywhere. These should never be hit under normal
> > > conditions, but let's play it safe for now.
> > > 
> > > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/intel_ddi.c | 25 ++++++++++++++++++++-----
> > >  1 file changed, 20 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> > > index f0a709b66e00..5f1c546e5e61 100644
> > > --- a/drivers/gpu/drm/i915/intel_ddi.c
> > > +++ b/drivers/gpu/drm/i915/intel_ddi.c
> > > @@ -801,6 +801,9 @@ static int intel_ddi_hdmi_level(struct drm_i915_private *dev_priv, enum port por
> > >  	    hdmi_level >= n_hdmi_entries)
> > >  		hdmi_level = hdmi_default_entry;
> > >  
> > > +	if (WARN_ON_ONCE(hdmi_level >= n_hdmi_entries))
> > > +		hdmi_level = n_hdmi_entries - 1;
> > 
> > intel_ddi_get_buf_trans_* can set n_entries to 0 on failure,
> > which would cause this to return a level of -1 - maybe those functions
> > need to return 1 on failure instead, similar to the cnl_get_buf_trans_*
> > functions?
> 
> Hmm. I guess we could just do
> 
> if (WARN_ON(hdmi_level == 0))
> 	return;
> 
> before the other check. That would be equivalent to the
> !ddi_translations checks done in the other places.

Hmm. Actually now that I read things again, the -1 shouldn't actually
cause us any problems since all uses of it would do a second
!ddi_translations check before indexing anything with the -1.

-1 and 0 are both wrong indexes when dealing with a zero sized array,
but I suppose in theory 0 is a bit better since it would trip up on
firther level>=n_entries checks. So I guess I could try to avoid
the negative value.

Another way to do that would be just
- return hdmi_level;
+ return max(hdmi_level, 0);

Or your other idea about keeping things unsigned would also take care
of it. Except having a wild UINT_MAX roaming around seems potentially
more dangerous to me.

> > 
> > > +
> > >  	return hdmi_level;
> > >  }
> > >  
> > > @@ -864,6 +867,11 @@ static void intel_prepare_hdmi_ddi_buffers(struct intel_encoder *encoder,
> > >  
> > >  	ddi_translations_hdmi = intel_ddi_get_buf_trans_hdmi(dev_priv, &n_hdmi_entries);
> > >  
> > > +	if (WARN_ON_ONCE(!ddi_translations_hdmi))
> > > +		return;
> > > +	if (WARN_ON_ONCE(hdmi_level >= n_hdmi_entries))
> > > +		hdmi_level = n_hdmi_entries - 1;
> > > +
> > >  	/* If we're boosting the current, set bit 31 of trans1 */
> > >  	if (IS_GEN9_BC(dev_priv) &&
> > >  	    dev_priv->vbt.ddi_port_info[port].hdmi_boost_level)
> > > @@ -1847,6 +1855,11 @@ static void skl_ddi_set_iboost(struct intel_encoder *encoder,
> > >  		else
> > >  			ddi_translations = intel_ddi_get_buf_trans_dp(dev_priv, port, &n_entries);
> > >  
> > > +		if (WARN_ON_ONCE(!ddi_translations))
> > > +			return;
> > > +		if (WARN_ON_ONCE(level >= n_entries))
> > > +			level = n_entries - 1;
> > 
> > 
> > > +
> > >  		iboost = ddi_translations[level].i_boost;
> > >  	}
> > >  
> > > @@ -1877,6 +1890,11 @@ static void bxt_ddi_vswing_sequence(struct intel_encoder *encoder,
> > >  	else
> > >  		ddi_translations = bxt_get_buf_trans_dp(dev_priv, &n_entries);
> > >  
> > > +	if (WARN_ON_ONCE(!ddi_translations))
> > > +		return;
> > > +	if (WARN_ON_ONCE(level >= n_entries))
> > > +		level = n_entries - 1;
> > > +
> > >  	bxt_ddi_phy_set_signal_level(dev_priv, port,
> > >  				     ddi_translations[level].margin,
> > >  				     ddi_translations[level].scale,
> > > @@ -1932,13 +1950,10 @@ static void cnl_ddi_vswing_program(struct intel_encoder *encoder,
> > >  	else
> > >  		ddi_translations = cnl_get_buf_trans_dp(dev_priv, &n_entries);
> > >  
> > > -	if (WARN_ON(ddi_translations == NULL))
> > > +	if (WARN_ON_ONCE(!ddi_translations))
> > >  		return;
> > > -
> > > -	if (level >= n_entries) {
> > > -		DRM_DEBUG_KMS("DDI translation not found for level %d. Using %d instead.", level, n_entries - 1);
> > > +	if (WARN_ON_ONCE(level >= n_entries))
> > >  		level = n_entries - 1;
> > > -	}
> > >  
> > >  	/* Set PORT_TX_DW5 Scaling Mode Sel to 010b. */
> > >  	val = I915_READ(CNL_PORT_TX_DW5_LN0(port));
> > > -- 
> > > 2.13.6
> > > 
> > > _______________________________________________
> > > Intel-gfx mailing list
> > > Intel-gfx@lists.freedesktop.org
> > > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Ville Syrjälä
> Intel OTC
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Ville Syrjälä
Intel OTC
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