[Intel-gfx] [PATCH] drm/i915/dp: DP PHY compliance for JSL

[Ville Syrjälä]

On Fri, Jun 12, 2020 at 11:25:42AM -0700, Manasi Navare wrote:
> On Fri, Jun 05, 2020 at 12:03:19AM +0300, Ville Syrjälä wrote:
> > On Thu, Jun 04, 2020 at 08:01:03PM +0000, Almahallawy, Khaled wrote:
> > > On Thu, 2020-06-04 at 22:06 +0300, Ville Syrjälä wrote:
> > > > On Thu, Jun 04, 2020 at 10:33:48AM +0530, Vidya Srinivas wrote:
> > > > > Signed-off-by: Khaled Almahallawy <khaled.almahallawy at intel.com>
> > > > > Signed-off-by: Vidya Srinivas <vidya.srinivas at intel.com>
> > > > > ---
> > > > >  drivers/gpu/drm/i915/display/intel_dp.c | 40
> > > > > ++++++++++++++++++++++++++-------
> > > > >  1 file changed, 32 insertions(+), 8 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> > > > > b/drivers/gpu/drm/i915/display/intel_dp.c
> > > > > index 7223367171d1..44663e8ac9a1 100644
> > > > > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > > > > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > > > > @@ -5470,22 +5470,32 @@ intel_dp_autotest_phy_ddi_disable(struct
> > > > > intel_dp *intel_dp)
> > > > >  	struct drm_i915_private *dev_priv = to_i915(dev);
> > > > >  	struct intel_crtc *crtc = to_intel_crtc(intel_dig_port-
> > > > > >base.base.crtc);
> > > > >  	enum pipe pipe = crtc->pipe;
> > > > > -	u32 trans_ddi_func_ctl_value, trans_conf_value,
> > > > > dp_tp_ctl_value;
> > > > > +	u32 trans_ddi_func_ctl_value, trans_conf_value,
> > > > > dp_tp_ctl_value, trans_ddi_port_mask;
> > > > > +	enum port port = intel_dig_port->base.port;
> > > > > +	i915_reg_t dp_tp_reg;
> > > > > +
> > > > > +	if (IS_ELKHARTLAKE(dev_priv)) {
> > > > > +		dp_tp_reg = DP_TP_CTL(port);
> > > > > +		trans_ddi_port_mask = TRANS_DDI_PORT_MASK;
> > > > > +	} else if (IS_TIGERLAKE(dev_priv)) {
> > > > > +		dp_tp_reg = TGL_DP_TP_CTL(pipe);
> > > > > +		trans_ddi_port_mask = TGL_TRANS_DDI_PORT_MASK;
> > > > > +	}
> > > > >  
> > > > >  	trans_ddi_func_ctl_value = intel_de_read(dev_priv,
> > > > >  						 TRANS_DDI_FUNC_CTL(pip
> > > > > e));
> > > > >  	trans_conf_value = intel_de_read(dev_priv, PIPECONF(pipe));
> > > > > -	dp_tp_ctl_value = intel_de_read(dev_priv, TGL_DP_TP_CTL(pipe));
> > > > >  
> > > > > +	dp_tp_ctl_value = intel_de_read(dev_priv, dp_tp_reg);
> > > > >  	trans_ddi_func_ctl_value &= ~(TRANS_DDI_FUNC_ENABLE |
> > > > > -				      TGL_TRANS_DDI_PORT_MASK);
> > > > > +					trans_ddi_port_mask);
> > > > >  	trans_conf_value &= ~PIPECONF_ENABLE;
> > > > >  	dp_tp_ctl_value &= ~DP_TP_CTL_ENABLE;
> > > > >  
> > > > >  	intel_de_write(dev_priv, PIPECONF(pipe), trans_conf_value);
> > > > >  	intel_de_write(dev_priv, TRANS_DDI_FUNC_CTL(pipe),
> > > > >  		       trans_ddi_func_ctl_value);
> > > > > -	intel_de_write(dev_priv, TGL_DP_TP_CTL(pipe), dp_tp_ctl_value);
> > > > > +	intel_de_write(dev_priv, dp_tp_reg, dp_tp_ctl_value);
> > > > 
> > > > All this ad-hoc modeset code really should not exist. It's going to
> > > > have different bugs than the norma modeset paths, so compliance
> > > > testing
> > > > this special code proves absolutely nothing about the normal modeset
> > > > code. IMO someone needs to take up the task of rewrtiting all this to
> > > > just perform normal modesets.
> > > 
> > > Agree. I've just found that we get kernel NULL pointer dereference and
> > > panic when we try to access to_intel_crtc(intel_dig_port-
> > > >base.base.crtc).
> > 
> > Yeah, that's a legacy pointer which should no longer be used at all
> > with atomic drivers. I'm slowly trying to clear out all this legacy
> > cruft. The next step I had hoped to take was
> > https://patchwork.freedesktop.org/series/76993/ but then this
> > compliacnce stuff landed and threw another wrench into the works.
> 
> We had several discussions on design of DP PHY compliance and the patches were on the M-L
> for quite some time without anyone giving feedback on the actual design of whether they should
> happen through modeset or directly from the PHY comp request short pulse.
> My first feedback was also that this should happen through a complete modeset where after we get
> PHY comp request we send a uevent like we do for link layer compliance and then trigger a full modeset.
> But honestly that was just a lot of overhead and 
> The reason we decided to go with this ad hoc approach was that with PHY compliance request,
> nothing really changes in terms of link parameters so we do not need to go through
> a complete modeset request unlike link layer compliance where we need to do compute config
> all over again to do the link params computation.
> 
> Every PHY comp request first sends a link layer comp request that does a full modeset
> and sets up the desired link rate/lane count.
> Then with PHY request, all we need to do is disable pipe conf, dp_tp_ctl, set the PHY patterns
> and renable the pipe conf and dp_tp_ctl without interfering and doing anything with a full modeset.
> 
> Now i think if we need to scale this to other platforms, can we add a per platform hook
> for handle_phy_request that gets the correct DP_TP_CTL etc and sets up the PHY patterns and
> reenables the already set link?
> 
> We have thoroughly tested this using the scopes and DPR 100 and it has been working correctly
> with the existing IGT compliance tool so IMO no need to rewrite the entire set of patches.
> 
> Ville, Khaled ?

You're just multiplying the amount of work and bugs we have
for every platform.

And as said testing some special compliance paths proves
pretty much nothing about the real code paths. So the only
point of that code AFAICS it to tick some "we haz
compliance code?" checkbox in some random spreadsheet instead
of actually providing evidence that our real code works
correctly.

-- 
Ville Syrjälä
Intel