Re: [PATCH] drm/i915/dp: Check for Low voltage IO only for eDP

["Nautiyal, Ankit K" <ankit.k.nautiyal@xxxxxxxxx>]

On 8/3/2022 7:45 PM, Jani Nikula wrote:
> On Tue, 26 Jul 2022, Ankit Nautiyal <ankit.k.nautiyal@xxxxxxxxx> wrote:
> > The low voltage sku check can be ignored as OEMs need to consider that
> > when designing the board and then put any limits in VBT.
> >
> > Due to this check many DP sink that can be run with higher link rate,
> > are run at lower link rate, thereby pruning the resolutions that are
> > intended to be working as per bspec.
> >
> > However, some eDP panels are getting issues [1] with higher link rate.
> > So keep the low voltage check for eDP, but ignore for DP sinks.
> What's the root cause? This seems like guess work.
>
> BR,
> Jani.

Hi Jani,

The root cause for the issue#6205 is still not known. I did find out a 
missing WA which seemed to be fixing flickers with eDP HBR3 panel.

https://patchwork.freedesktop.org/patch/496283/?series=106967&rev=1

But it doesn't solve the issue 
https://gitlab.freedesktop.org/drm/intel/-/issues/6205 .

As you know, the low voltage sku check for combo phy port is not 
required as bspec says this should be handled in VBT but removing the 
check perhaps exposed the above issue seen on eDP.

Does it make any sense to have the low voltage sku check removed for DP, 
till we get root cause for the eDP ?

Regards,

Ankit

> > [1] https://gitlab.freedesktop.org/drm/intel/-/issues/6205
> >
> > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5272
> >
> > v2: Added comment about eDP HBR2 restriction for JSL/EHL (Arun).
> >
> > Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@xxxxxxxxx>
> > Reviewed-by: Arun R Murthy <arun.r.murthy@xxxxxxxxx>
> > ---
> >   drivers/gpu/drm/i915/display/intel_dp.c | 14 +++++++-------
> >   1 file changed, 7 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 32292c0be2bd..e50bba14e8c5 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -405,7 +405,8 @@ static int icl_max_source_rate(struct intel_dp *intel_dp)
> >   	enum phy phy = intel_port_to_phy(dev_priv, dig_port->base.port);
> >   
> >   	if (intel_phy_is_combo(dev_priv, phy) &&
> > -	    (is_low_voltage_sku(dev_priv, phy) || !intel_dp_is_edp(intel_dp)))
> > +	    intel_dp_is_edp(intel_dp) &&
> > +	    is_low_voltage_sku(dev_priv, phy))
> >   		return 540000;
> >   
> >   	return 810000;
> > @@ -413,11 +414,8 @@ static int icl_max_source_rate(struct intel_dp *intel_dp)
> >   
> >   static int ehl_max_source_rate(struct intel_dp *intel_dp)
> >   {
> > -	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
> > -	struct drm_i915_private *dev_priv = to_i915(dig_port->base.base.dev);
> > -	enum phy phy = intel_port_to_phy(dev_priv, dig_port->base.port);
> > -
> > -	if (intel_dp_is_edp(intel_dp) || is_low_voltage_sku(dev_priv, phy))
> > +	/* For JSL/EHL, eDP supports only HBR2 5.4 (SOC PHY restriction) */
> > +	if (intel_dp_is_edp(intel_dp))
> >   		return 540000;
> >   
> >   	return 810000;
> > @@ -429,7 +427,9 @@ static int dg1_max_source_rate(struct intel_dp *intel_dp)
> >   	struct drm_i915_private *i915 = to_i915(dig_port->base.base.dev);
> >   	enum phy phy = intel_port_to_phy(i915, dig_port->base.port);
> >   
> > -	if (intel_phy_is_combo(i915, phy) && is_low_voltage_sku(i915, phy))
> > +	if (intel_phy_is_combo(i915, phy) &&
> > +	    intel_dp_is_edp(intel_dp) &&
> > +	    is_low_voltage_sku(i915, phy))
> >   		return 540000;
> >   
> >   	return 810000;