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

["Kulkarni, Vandita" <vandita.kulkarni@intel.com>]

> -----Original Message-----
> From: Intel-gfx <intel-gfx-bounces@lists.freedesktop.org> On Behalf Of
> Kulkarni, Vandita
> Sent: Tuesday, November 2, 2021 5:13 PM
> To: Nikula, Jani <jani.nikula@intel.com>; intel-gfx@lists.freedesktop.org
> Subject: Re: [Intel-gfx] [V2 4/4] drm/i915/dsi: Ungate clock before enabling the
> phy
> 
> > -----Original Message-----
> > From: Nikula, Jani <jani.nikula@intel.com>
> > Sent: Tuesday, November 2, 2021 3:13 PM
> > To: Kulkarni, Vandita <vandita.kulkarni@intel.com>; intel-
> > gfx@lists.freedesktop.org
> > Cc: Deak, Imre <imre.deak@intel.com>; Roper, Matthew D
> > <matthew.d.roper@intel.com>; ville.syrjala@linux.intel.com
> > Subject: RE: [V2 4/4] drm/i915/dsi: Ungate clock before enabling the
> > phy
> >
> > On Tue, 02 Nov 2021, "Kulkarni, Vandita" <vandita.kulkarni@intel.com>
> > wrote:
> > >> -----Original Message-----
> > >> From: Nikula, Jani <jani.nikula@intel.com>
> > >> Sent: Monday, November 1, 2021 5:37 PM
> > >> To: Kulkarni, Vandita <vandita.kulkarni@intel.com>; intel-
> > >> gfx@lists.freedesktop.org
> > >> Cc: Deak, Imre <imre.deak@intel.com>; Roper, Matthew D
> > >> <matthew.d.roper@intel.com>; ville.syrjala@linux.intel.com
> > >> Subject: RE: [V2 4/4] drm/i915/dsi: Ungate clock before enabling
> > >> the phy
> > >>
> > >> On Thu, 28 Oct 2021, "Kulkarni, Vandita"
> > >> <vandita.kulkarni@intel.com>
> > >> wrote:
> > >> >> -----Original Message-----
> > >> >> From: Nikula, Jani <jani.nikula@intel.com>
> > >> >> Sent: Thursday, October 28, 2021 8:06 PM
> > >> >> To: Kulkarni, Vandita <vandita.kulkarni@intel.com>; intel-
> > >> >> gfx@lists.freedesktop.org
> > >> >> Cc: Deak, Imre <imre.deak@intel.com>; Roper, Matthew D
> > >> >> <matthew.d.roper@intel.com>; ville.syrjala@linux.intel.com
> > >> >> Subject: RE: [V2 4/4] drm/i915/dsi: Ungate clock before enabling
> > >> >> the phy
> > >> >>
> > >> >> On Thu, 28 Oct 2021, "Kulkarni, Vandita"
> > >> >> <vandita.kulkarni@intel.com>
> > >> >> wrote:
> > >> >> >> -----Original Message-----
> > >> >> >> From: Nikula, Jani <jani.nikula@intel.com>
> > >> >> >> Sent: Thursday, October 28, 2021 5:13 PM
> > >> >> >> To: Kulkarni, Vandita <vandita.kulkarni@intel.com>; intel-
> > >> >> >> gfx@lists.freedesktop.org
> > >> >> >> Cc: Deak, Imre <imre.deak@intel.com>; Roper, Matthew D
> > >> >> >> <matthew.d.roper@intel.com>; ville.syrjala@linux.intel.com;
> > >> >> >> Kulkarni, Vandita <vandita.kulkarni@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@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@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?
> > >> >>
> > >> >> I'm just royally confused about the sequence myself, so I'm
> > >> >> asking you. ;)
> > >> >>
> > >> >> It doesn't help that the code has step references to gen 11 mode
> > >> >> set that are completely different from the steps in gen 12 sequence.
> > >> >
> > >> > Right, they have lot of different steps coming in.
> > >> > As per gen11 sequence, we were gating pll after enabling ddi buffer.
> > >> >
> > >> > Initially when there was only gen12 in the bspec, it stated to
> > >> > gate the pll
> > >> after mapping.
> > >> > Hence we had that commit  991d9557b0c4.
> > >> > Then Gen12's mipi dsi sequence was carried fwd for all later
> > >> > platforms as
> > >> well.
> > >> >  with the modification saying that Do not gate the pll until we
> > >> > enable the ddi buffer.
> > >> > And this applies to gen 12 as well because they have marked the
> > >> > earlier mentioned step of gating pll after pll mapping as removed
> > >> > on all
> > >> gen12 and later platforms.
> > >> >
> > >> > This patch now is keeping the older step as is, but making sure
> > >> > that clocks
> > >> are ungated while enabling ddi buffer.
> > >>
> > >> Where does it say for gen12+ that clocks should be ungated at any point?
> > >>
> > >> My reading of the spec:
> > >>
> > >> Gen11, bspec 20845 and 20597:
> > >> - start with clocks ungated at mapping
> > >> - gate after port/phy enabling (step 4m in gen11 mode set sequence)
> > >>
> > >> Gen12, bspec 49204, 49188 and 55316:
> > >> - start with clocks gated at mapping
> > >> - gate *if* not already gated (steps 4c and 4i in gen12 mode set
> > >> sequence)
> > >
> > > Right the ungate step is not mentioned in the bspec.
> > > Instead the step 4.c is marked as Removed.
> > > I had added ungate just to make sure we are addressing the issue
> > > mentioned in front of removed tag while Retaining the old sequence
> > > of 4.c
> > >
> > > In order to completely adhere to the current bspec, I can 1. submit
> > > a patch removing 4.c or 2.  submit a revert of the patch which was
> > > adding 4.c
> > > ("drm/i915/tgl/dsi: Gate the ddi clocks after pll mapping")
> >
> > I think if you remove the call to gen11_dsi_ungate_clocks(encoder)
> > from this patch, the sequence matches bspec.
> >
> > But this means the sequence is different between display 11 and 12+,
> > and the clock will be gated for the entire enabling sequence on 12+.
> > That's my reading of bspec, anyway.
> 
> Right the current bspec doesn't show us where to enable the clocks.
> Clock ungating is not mentioned anywhere, and we need to enable clocks
> before enabling DDI_BUF_CTL , have requested for sequence update in the
> bspec.
As per the lates tbspec update, have floated the revert of 
("drm/i915/tgl/dsi: Gate the ddi clocks after pll mapping")

This patch can be ignored now.

Thanks,
Vandita
> 
> Thanks,
> Vandita
> >
> > BR,
> > Jani.
> >
> >
> >
> > >
> > > Thanks,
> > > Vandita
> > >>
> > >> It may be that your patch is correct, but IMO it does not match bspec.
> > >>
> > >>
> > >> BR,
> > >> Jani.
> > >>
> > >>
> > >>
> > >> >
> > >> > Thanks
> > >> > Vandita
> > >> >>
> > >> >> BR,
> > >> >> Jani.
> > >> >>
> > >> >>
> > >> >>
> > >> >> >
> > >> >> > 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
> > >> >>
> > >> >> --
> > >> >> Jani Nikula, Intel Open Source Graphics Center
> > >>
> > >> --
> > >> Jani Nikula, Intel Open Source Graphics Center
> >
> > --
> > Jani Nikula, Intel Open Source Graphics Center