[Intel-gfx] [V2 4/4] drm/i915/dsi: Ungate clock before enabling the phy

[Kulkarni, Vandita]

> -----Original Message-----
> From: Nikula, Jani <jani.nikula at intel.com>
> Sent: Thursday, October 28, 2021 5:13 PM
> To: Kulkarni, Vandita <vandita.kulkarni at intel.com>; intel-
> gfx at lists.freedesktop.org
> Cc: Deak, Imre <imre.deak at intel.com>; Roper, Matthew D
> <matthew.d.roper at intel.com>; ville.syrjala at linux.intel.com; Kulkarni,
> Vandita <vandita.kulkarni at intel.com>
> Subject: Re: [V2 4/4] drm/i915/dsi: Ungate clock before enabling the phy
> 
> On Tue, 19 Oct 2021, Vandita Kulkarni <vandita.kulkarni at intel.com> wrote:
> > For the PHY enable/disable signalling to propagate between Dispaly and
> > PHY, DDI clocks need to be running when enabling the PHY.
> >
> > Bspec: 49188 says gate the clocks after enabling the
> >        DDI Buffer.
> >        We also have a commit 991d9557b0c4 ("drm/i915/tgl/dsi: Gate the ddi
> >        clocks after pll mapping") which gates the clocks much before,
> >        as per the older spec. This commit nullifies its effect and makes
> >        sure that the clocks are not gated while we enable the DDI
> >        buffer.
> > v2: Bspec ref, add a comment wrt earlier clock gating sequence (Jani)
> >
> > Signed-off-by: Vandita Kulkarni <vandita.kulkarni at intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/icl_dsi.c | 8 +++-----
> >  1 file changed, 3 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/icl_dsi.c
> > b/drivers/gpu/drm/i915/display/icl_dsi.c
> > index 63dd75c6448a..e5ef5c4a32d7 100644
> > --- a/drivers/gpu/drm/i915/display/icl_dsi.c
> > +++ b/drivers/gpu/drm/i915/display/icl_dsi.c
> > @@ -1135,8 +1135,6 @@ static void
> >  gen11_dsi_enable_port_and_phy(struct intel_encoder *encoder,
> >  			      const struct intel_crtc_state *crtc_state)  {
> > -	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
> > -
> >  	/* step 4a: power up all lanes of the DDI used by DSI */
> >  	gen11_dsi_power_up_lanes(encoder);
> >
> > @@ -1146,6 +1144,8 @@ gen11_dsi_enable_port_and_phy(struct
> intel_encoder *encoder,
> >  	/* step 4c: configure voltage swing and skew */
> >  	gen11_dsi_voltage_swing_program_seq(encoder);
> >
> > +	gen11_dsi_ungate_clocks(encoder);
> > +
> 
> What about the changes to gen11_dsi_map_pll() in commit 991d9557b0c4
> ("drm/i915/tgl/dsi: Gate the ddi clocks after pll mapping")? It starts off with
> clocks gated for gen12+, ungated otherwise.

Now the same spec is updated with the gate step after ddi buffer enable.
And the one before is marked with remove tag.
That makes all gen12+ align with gen 11.
You suggested to update the same in the commit message on v1.
Should I still consider just reverting that commit?

Thanks,
Vandita

> 
> BR,
> Jani.
> 
> 
> >  	/* enable DDI buffer */
> >  	gen11_dsi_enable_ddi_buffer(encoder);
> >
> > @@ -1161,9 +1161,7 @@ gen11_dsi_enable_port_and_phy(struct
> intel_encoder *encoder,
> >  	/* Step (4h, 4i, 4j, 4k): Configure transcoder */
> >  	gen11_dsi_configure_transcoder(encoder, crtc_state);
> >
> > -	/* Step 4l: Gate DDI clocks */
> > -	if (DISPLAY_VER(dev_priv) == 11)
> > -		gen11_dsi_gate_clocks(encoder);
> > +	gen11_dsi_gate_clocks(encoder);
> >  }
> >
> >  static void gen11_dsi_powerup_panel(struct intel_encoder *encoder)
> 
> --
> Jani Nikula, Intel Open Source Graphics Center