Re: [Intel-gfx] [PATCH 1/3] drm/i915/display: Load DP_TP_CTL/STATUS offset before use it

["Souza, Jose" <jose.souza@intel.com>]

On Wed, 2020-04-15 at 20:56 -0700, Matt Roper wrote:
> On Tue, Apr 14, 2020 at 04:04:40PM -0700, José Roberto de Souza
> wrote:
> > Right now dp.regs.dp_tp_ctl/status are only set during the encoder
> > pre_enable() hook, what is causing all reads and writes to those
> > registers to go to offset 0x0 before pre_enable() is executed.
> > 
> > So if i915 takes the BIOS state and don't do a modeset any
> > following
> > link retraing will fail.
> > 
> > In the case that i915 needs to do a modeset, the DDI disable
> > sequence
> > will write to a wrong register not disabling DP 'Transport Enable'
> > in
> > DP_TP_CTL, making a HDMI modeset in the same port/transcoder to
> > not light up the monitor.
> 
> So to clarify I understand the problematic sequence properly:
>  * i915 inherits already-enabled display from BIOS; pre_enable is
> never
>    called
>  * we do a modeset, so we have to disable the display and then try to
> re-enable
>      - intel_disable_ddi_buf() writes to offset 0 rather than the
> proper
>        register offset when attempting to reprogram DP_TP_CTL and
>        disable DP
>      - when we re-enable, the old, still-active DP settings in
> hardware
>        cause problems and the display doesn't light up
> 
> A couple clarifying questions:
>  - It seems like we should have seen unclaimed register warnings from
>    the bogus writes to offset 0 during disable.  Any idea why those
>    didn't show up?

Offset 0x0 is valid BSpec: 29316

>  - In the commit message you mention that it's the DP Transport
> Enable
>    that's the culprit here, which breaks future attempts to light up
>    HDMI.   I assume this means that we're also switching which pipe
>    we're driving the port with, not just doing any
> modeset?  Otherwise
>    DP would stay DP, HDMI would stay HDMI, and we wouldn't see this
>    problem with DP being active on an HDMI monitor (although we'd
> still
>    be writing to an invalid register offset during our first DP
> disable
>    which might cause other problems).  Might be worth adding a
> mention
>    of the pipe change to the commit message to clarify.

Got this state in a system were BIOS is lighing up DP in pipe B when
HDMI is also connected and leaving pipe A off, no idea why BIOS decided
this.
But when i915 takes over we do the modeset to light up HDMI and
reorder the pipes.

> 
> The changes here look correct to me; we'll ensure the DP registers
> have
> proper offsets before we do our first modeset, and then the rest of
> the
> runtime behavior thereafter should be unchanged.  So
> 
> Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
> 
> 
> > So here for GENs older than 12, that have those registers fixed at
> > port offset range it is loading at encoder/port init while for
> > GEN12
> > it will keep setting it at encoder pre_enable() and during HW state
> > readout.
> > 
> > Fixes: 4444df6e205b ("drm/i915/tgl: move DP_TP_* to transcoder")
> > Cc: Matt Roper <matthew.d.roper@intel.com>
> > Cc: Lucas De Marchi <lucas.demarchi@intel.com>
> > Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_ddi.c | 14 +++++++++++---
> >  drivers/gpu/drm/i915/display/intel_dp.c  |  5 ++---
> >  2 files changed, 13 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c
> > b/drivers/gpu/drm/i915/display/intel_ddi.c
> > index be6c61bcbc9c..1aab93a94f40 100644
> > --- a/drivers/gpu/drm/i915/display/intel_ddi.c
> > +++ b/drivers/gpu/drm/i915/display/intel_ddi.c
> > @@ -3252,9 +3252,6 @@ static void hsw_ddi_pre_enable_dp(struct
> > intel_atomic_state *state,
> >  	intel_dp_set_link_params(intel_dp, crtc_state->port_clock,
> >  				 crtc_state->lane_count, is_mst);
> >  
> > -	intel_dp->regs.dp_tp_ctl = DP_TP_CTL(port);
> > -	intel_dp->regs.dp_tp_status = DP_TP_STATUS(port);
> > -
> >  	intel_edp_panel_on(intel_dp);
> >  
> >  	intel_ddi_clk_select(encoder, crtc_state);
> > @@ -4061,12 +4058,18 @@ void intel_ddi_get_config(struct
> > intel_encoder *encoder,
> >  	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
> >  	struct intel_crtc *intel_crtc = to_intel_crtc(pipe_config-
> > >uapi.crtc);
> >  	enum transcoder cpu_transcoder = pipe_config->cpu_transcoder;
> > +	struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
> >  	u32 temp, flags = 0;
> >  
> >  	/* XXX: DSI transcoder paranoia */
> >  	if (drm_WARN_ON(&dev_priv->drm,
> > transcoder_is_dsi(cpu_transcoder)))
> >  		return;
> >  
> > +	if (INTEL_GEN(dev_priv) >= 12) {
> > +		intel_dp->regs.dp_tp_ctl =
> > TGL_DP_TP_CTL(cpu_transcoder);
> > +		intel_dp->regs.dp_tp_status =
> > TGL_DP_TP_STATUS(cpu_transcoder);
> > +	}
> > +
> >  	intel_dsc_get_config(encoder, pipe_config);
> >  
> >  	temp = intel_de_read(dev_priv,
> > TRANS_DDI_FUNC_CTL(cpu_transcoder));
> > @@ -4396,6 +4399,7 @@ static const struct drm_encoder_funcs
> > intel_ddi_funcs = {
> >  static struct intel_connector *
> >  intel_ddi_init_dp_connector(struct intel_digital_port
> > *intel_dig_port)
> >  {
> > +	struct drm_i915_private *dev_priv = to_i915(intel_dig_port-
> > >base.base.dev);
> >  	struct intel_connector *connector;
> >  	enum port port = intel_dig_port->base.port;
> >  
> > @@ -4406,6 +4410,10 @@ intel_ddi_init_dp_connector(struct
> > intel_digital_port *intel_dig_port)
> >  	intel_dig_port->dp.output_reg = DDI_BUF_CTL(port);
> >  	intel_dig_port->dp.prepare_link_retrain =
> >  		intel_ddi_prepare_link_retrain;
> > +	if (INTEL_GEN(dev_priv) < 12) {
> > +		intel_dig_port->dp.regs.dp_tp_ctl = DP_TP_CTL(port);
> > +		intel_dig_port->dp.regs.dp_tp_status =
> > DP_TP_STATUS(port);
> > +	}
> >  
> >  	if (!intel_dp_init_connector(intel_dig_port, connector)) {
> >  		kfree(connector);
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> > b/drivers/gpu/drm/i915/display/intel_dp.c
> > index d4fcc9583869..03591ab76b0d 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -2671,9 +2671,6 @@ static void intel_dp_prepare(struct
> > intel_encoder *encoder,
> >  				 intel_crtc_has_type(pipe_config,
> >  						     INTEL_OUTPUT_DP_MS
> > T));
> >  
> > -	intel_dp->regs.dp_tp_ctl = DP_TP_CTL(port);
> > -	intel_dp->regs.dp_tp_status = DP_TP_STATUS(port);
> > -
> >  	/*
> >  	 * There are four kinds of DP registers:
> >  	 *
> > @@ -8470,6 +8467,8 @@ bool intel_dp_init(struct drm_i915_private
> > *dev_priv,
> >  
> >  	intel_dig_port->dp.output_reg = output_reg;
> >  	intel_dig_port->max_lanes = 4;
> > +	intel_dig_port->dp.regs.dp_tp_ctl = DP_TP_CTL(port);
> > +	intel_dig_port->dp.regs.dp_tp_status = DP_TP_STATUS(port);
> >  
> >  	intel_encoder->type = INTEL_OUTPUT_DP;
> >  	intel_encoder->power_domain = intel_port_to_power_domain(port);
> > -- 
> > 2.26.0
> > 
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