Re: [PATCH 7/6] drm/i915/skl: DDI-E and DDI-A shares 4 lanes.

["Vivi, Rodrigo" <rodrigo.vivi@intel.com>]

On Thu, 2015-08-27 at 17:31 +0300, Timo Aaltonen wrote:
> On 27.08.2015 05:52, Zhang, Xiong Y wrote:
> > > On Wed, 2015-08-26 at 11:15 +0300, Jani Nikula wrote:
> > > > On Thu, 13 Aug 2015, "Jindal, Sonika" <sonika.jindal@intel.com>
> > > > wrote:
> > > > > On 8/13/2015 8:57 AM, Zhang, Xiong Y wrote:
> > > > > > > On Wed, 2015-08-12 at 02:20 +0000, Zhang, Xiong Y wrote:
> > > > > > > > > On Tue, 2015-08-11 at 07:05 +0000, Zhang, Xiong Y 
> > > > > > > > > wrote:
> > > > > > > > > > > -----Original Message-----
> > > > > > > > > > > From: Vivi, Rodrigo
> > > > > > > > > > > Sent: Saturday, August 8, 2015 8:34 AM
> > > > > > > > > > > To: intel-gfx@lists.freedesktop.org
> > > > > > > > > > > Cc: Vivi, Rodrigo; Zhang, Xiong Y
> > > > > > > > > > > Subject: [PATCH 7/6] drm/i915/skl: DDI-E and DDI
> > > > > > > > > > > -A
> > > > > > > > > > > shares 4
> > > > > > > > > > > lanes.
> > > > > > > > > > > 
> > > > > > > > > > > DDI-A and DDI-E shares the 4 lanes. So when DDI-E 
> > > > > > > > > > > is
> > > > > > > > > > > present we
> > > > > > > > > > > need to configure lane count propperly for both.
> > > > > > > > > > > 
> > > > > > > > > > > This was based on Sonika's
> > > > > > > > > > > [PATCH] drm/i915/skl: Select DDIA lane capability 
> > > > > > > > > > > based
> > > > > > > > > > > upon vbt
> > > > > > > > > > > 
> > > > > > > > > > > Credits-to: Sonika Jindal <
> > > > > > > > > > > sonika.jindal@intel.com>
> > > > > > > > > > > Cc: Xiong Zhang <xiong.y.zhang@intel.com>
> > > > > > > > > > > Signed-off-by: Rodrigo Vivi <
> > > > > > > > > > > rodrigo.vivi@intel.com>
> > > > > > > > > > > ---
> > > > > > > > > > >   drivers/gpu/drm/i915/intel_ddi.c | 12 
> > > > > > > > > > > ++++++++++--
> > > > > > > > > > > drivers/gpu/drm/i915/intel_dp.c  |  8 +++++---
> > > > > > > > > > >   2 files changed, 15 insertions(+), 5 deletions(
> > > > > > > > > > > -)
> > > > > > > > > > > 
> > > > > > > > > > > diff --git a/drivers/gpu/drm/i915/intel_ddi.c
> > > > > > > > > > > b/drivers/gpu/drm/i915/intel_ddi.c
> > > > > > > > > > > index 110d546..557cecf 100644
> > > > > > > > > > > --- a/drivers/gpu/drm/i915/intel_ddi.c
> > > > > > > > > > > +++ b/drivers/gpu/drm/i915/intel_ddi.c
> > > > > > > > > > > @@ -3178,7 +3178,15 @@ void intel_ddi_init(struct
> > > > > > > > > > > drm_device
> > > > > > > > > > > *dev, enum port port)
> > > > > > > > > > >   	struct intel_digital_port 
> > > > > > > > > > > *intel_dig_port;
> > > > > > > > > > >   	struct intel_encoder *intel_encoder;
> > > > > > > > > > >   	struct drm_encoder *encoder;
> > > > > > > > > > > -	bool init_hdmi, init_dp;
> > > > > > > > > > > +	bool init_hdmi, init_dp, ddi_e_present;
> > > > > > > > > > > +
> > > > > > > > > > > +	/*
> > > > > > > > > > > +	 * On SKL we don't have a way to detect 
> > > > > > > > > > > DDI-E
> > > > > > > > > > > so we
> > > > > > > > > > > rely
> > > > > > > > > > > on VBT.
> > > > > > > > > > > +	 */
> > > > > > > > > > > +	ddie_present = IS_SKYLAKE(dev) &&
> > > > > > > > > > > +		(dev_priv
> > > > > > > > > > > ->vbt.ddi_port_info[PORT_E].supports_dp
> > > > > > > > > > > > > 
> > > > > > > > > > > +		 dev_priv
> > > > > > > > > > > ->vbt.ddi_port_info[PORT_E].supports_dvi
> > > > > > > > > > > > > 
> > > > > > > > > > > +		 dev_priv
> > > > > > > > > > > ->vbt.ddi_port_info[PORT_E].supports_hdmi);
> > > > > > > > > > [Zhang, Xiong Y]  ddie_present should be 
> > > > > > > > > > ddi_e_present
> > > > > > > > > > > 
> > > > > > > > > > >   	init_hdmi = (dev_priv
> > > > > > > > > > > ->vbt.ddi_port_info[port].supports_dvi ||
> > > > > > > > > > >   		     dev_priv
> > > > > > > > > > > ->vbt.ddi_port_info[port].supports_hdmi);
> > > > > > > > > > > @@ -3210,7 +3218,7 @@ void intel_ddi_init(struct
> > > > > > > > > > > drm_device
> > > > > > > > > > > *dev, enum port port)
> > > > > > > > > > >   	intel_dig_port->port = port;
> > > > > > > > > > >   	intel_dig_port->saved_port_bits =
> > > > > > > > > > > I915_READ(DDI_BUF_CTL(port)) &
> > > > > > > > > > > 
> > > > > > > > > > >   (DDI_BUF_PORT_REVERSAL |
> > > > > > > > > > > -
> > > > > > > > > > >  DDI_A_4_LANES);
> > > > > > > > > > > +
> > > > > > > > > > >  ddi_e_present ? 0 :
> > > > > > > > > > > DDI_A_4_LANES);
> > > > > > > > > > [Zhang, Xiong Y] Sonika's patch will set DDI-A to 4 
> > > > > > > > > > lanes
> > > > > > > > > > when
> > > > > > > > > > DDI-E doesn't exist, I think your patch will do 
> > > > > > > > > > nothing.
> > > > > > > > > 
> > > > > > > > > Actually DDI_A_4_LANES is being already set
> > > > > > > > > unconditionally, so
> > > > > > > > > Sonika's patch has no effect.
> > > > > > > > [Zhang, Xiong Y] No. Sonika's patch set DDI_A_4_LANES 
> > > > > > > > under
> > > > > > > > many
> > > > > > > > conditions.
> > > > > > > > +	if (IS_SKYLAKE(dev) && port == PORT_A
> > > > > > > > +		&& !(val & DDI_BUF_CTL_ENABLE)
> > > > > > > > +		&& !dev_priv->vbt.ddi_e_used)
> > > > > > > > +		I915_WRITE(DDI_BUF_CTL(port), val |
> > > > > > > > DDI_A_4_LANES)
> > > > > > > > > 
> > > > > > > > > saved_port_bits goes to intel_dp->DP that goes to
> > > > > > > > > DDI_BUF_CTL and
> > > > > > > > > also it is used to calculate the number of lanes.
> > > > > > > > > 
> > > > > > > > > With this patch we stop setting DDI_A_4_LANES when 
> > > > > > > > > ddi_e is
> > > > > > > > > present
> > > > > > > > > so DDI-A keeps with 2 lanes and let other 2 lanes for 
> > > > > > > > > DDI-E
> > > > > > > > [Zhang, Xiong Y] Yes, this patch will clear 
> > > > > > > > DDI_A_4_LANES
> > > > > > > > when ddi_e
> > > > > > > > is present.
> > > > > > > > But this patch won't set DDI_A_4_LANES under following
> > > > > > > > conditions
> > > > > > > > which is purpose for Sonika patch 1. Bios fail to 
> > > > > > > > driver eDP
> > > > > > > > and
> > > > > > > > doesn't enable DDI_A buffer
> > > > > > > 
> > > > > > > If DDI_A isn't enabled we don't need to set DDI_A_4_LANES
> > > > > > [Zhang, Xiong Y] From commit message on Sonika patch, she 
> > > > > > want to
> > > > > > set DDI_A_4_LANES on such case. Maybe she met such fail 
> > > > > > case on
> > > > > > one high
> > > > > > resolution eDP screen. Let's Sonikia explain it.
> > > > > > > 
> > > > > > > > 2. Bios clear DDI_A_4_LANES
> > > > > > > > 3. DDI_E isn't present
> > > > > > > 
> > > > > > > I don't agree... This is already covered on current code.
> > > > > > > DDI_A_4_LANES is
> > > > > > > already being set when enabling DDI_A.
> > > > > > > 
> > > > > As Zhang mentioned and as my commit message explains, my 
> > > > > patch is
> > > > > needed
> > > > > when bios failed to drive edp (In my case it was an 
> > > > > intermediate
> > > > > frequency supported panel which was set to 3.24 GHz and bios 
> > > > > didn't
> > > > > have
> > > > > support for intermediate frequencies), it will not enable 
> > > > > DDIA in
> > > > > which
> > > > > case, it will not set DDI_BUF_CTL and DDI Lane capability 
> > > > > will
> > > > > remain 0
> > > > > (which is DDIA with 2 lanes and DDIE with 2 lanes).
> > > > > So, since the native resolution of that panel was high and 
> > > > > couldn't
> > > > > work
> > > > > with 2 lanes.
> > > > > So, ideally we should not rely on bios to set the initial 
> > > > > value and
> > > > > set
> > > > > it based upon whether DDI_E is used or not.
> > > > > So, my patch has some effect :)
> > > > 
> > > > Rodrigo? Please figure out what the needed patch is, and send 
> > > > it.
> > > 
> > > I've just read Sonika's patch again to see if I could convince 
> > > myself
> > > to stop being stubborn...
> > > 
> > > I realized that our patches are independent. I still believe we 
> > > need
> > > this one here... We just need a reviewer.
> > > 
> > > But I'm really a stubborn and I'm not convinced we need the other
> > > patch. I still can't see how we would end up enabling DDI-A 
> > > without
> > > setting the lanes. For me if we don't call intel_ddi_init(port_A) 
> > > we
> > > don't need to set lanes or there is something else really wrong, 
> > > and if
> > > we call it this bit will be *always* set already.
> > [Zhang, Xiong Y] From Sonika experience, "always" isn't true 
> > because bios fail in initialize eDP.
> > In a short, if DDI-E is present, we should clear DDI_A_4_LANES, 
> > your patch will do this.
> > If DDI-E isn't present, we should set DDI_A_4_LANES, Sonika's patch 
> > will do it, but your patch miss it.

so I believe what I still can't understand is why we need to set
DDI_A_4_LANES when not using DDI_A... 

> > If you think your and Sonika's patch are independent, you could 
> > resend your patch with modified commit message.
> 
> If it helps with the debate, this patch caused a regression on an I+N
> hybrid machine where the display remained black after booting up..

... but nevermind... Apparently my patch is wrong and causing trouble
more than helping...

Thanks Timo.

> 
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