[Intel-gfx] [PATCH 07/13] drm/i915/cnl: DVFS for PLL enabling

[Rodrigo Vivi]

On Tue, Oct 17, 2017 at 03:44:21PM +0000, Ville Syrjälä wrote:
> On Tue, Oct 03, 2017 at 12:06:08AM -0700, Rodrigo Vivi wrote:
> > From: "Kahola, Mika" <mika.kahola at intel.com>
> > 
> > Display Voltage and Frequency Switching (DVFS) is used to adjust the
> > display voltage to match the display clock frequencies. If voltage is
> > set too low, it will break functionality. If voltage is set too high,
> > it will waste power. Voltage level is selected based on CD clock and
> > DDI clock.
> > 
> > The sequence before frequency change is the following and it requests
> > the power controller to raise voltage to maximum
> > 
> > - Ensure any previous GT Driver Mailbox transaction is complete.
> > - Write GT Driver Mailbox Data Low = 0x3.
> > - Write GT Driver Mailbox Data High = 0x0.
> > - Write GT Driver Mailbox Interface = 0x80000007.
> > - Poll GT Driver Mailbox Interface for Run/Busy indication cleared (bit 31 = 0).
> > - Read GT Driver Mailbox Data Low, if bit 0 is 0x1, continue, else restart the sequence.
> >   Timeout after 3ms
> > 
> > The sequence after frequency change is the following and it requests
> > the port controller to raise voltage to the requested level.
> > 
> > - Write GT Driver Mailbox Data Low
> >  * For level 0, write 0x0
> >  * For level 1, write 0x1
> >  * For level 2, write 0x2
> >  * For level 3, write 0x3
> >    - Write GT Driver Mailbox Data High = 0x0.
> >    - Write GT Driver Mailbox Interface = 0x80000007.
> > 
> > For Cannonlake, the level 3 is not used and it aliases to level 2.
> > 
> > v2: reuse Paulo's work on cdclk. This patch depends on Paulo's patch
> >     [PATCH 02/12] drm/i915/cnl: extract cnl_dvfs_{pre,post}_change
> > v3: (By Rodrigo): Remove duplicated commend and fix typo on Paulo's name.
> > v4: (By Rodrigo): Rebase on top "Unify and export gen9+ port_clock calculation"
> >     The port clock calculation here was only addressing DP, so let's reuse
> >     the current port calculation that is already in place without any duplication.
> >     Alos fix portclk <= 594000 instead of portclk < 594000.
> > 
> > Cc: Paulo Zanoni <paulo.r.zanoni at intel.com>
> > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > Signed-off-by: Kahola, Mika <mika.kahola at intel.com>
> > Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dpll_mgr.c | 30 ++++++++++++++++++++++--------
> >  1 file changed, 22 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dpll_mgr.c b/drivers/gpu/drm/i915/intel_dpll_mgr.c
> > index a2a3d93d67bd..6030fbafa580 100644
> > --- a/drivers/gpu/drm/i915/intel_dpll_mgr.c
> > +++ b/drivers/gpu/drm/i915/intel_dpll_mgr.c
> > @@ -1966,10 +1966,23 @@ static const struct intel_dpll_mgr bxt_pll_mgr = {
> >  	.dump_hw_state = bxt_dump_hw_state,
> >  };
> >  
> > +static int cnl_get_dvfs_level(int cdclk, int portclk)
> > +{
> > +	if (cdclk == 168000 && portclk <= 594000)
> > +		return 0;
> > +	else if (cdclk == 336000 && portclk <= 594000)
> > +		return 1;
> > +	else
> > +		return 2;
> > +}
> > +
> >  static void cnl_ddi_pll_enable(struct drm_i915_private *dev_priv,
> >  			       struct intel_shared_dpll *pll)
> >  {
> >  	uint32_t val;
> > +	int ret;
> > +	int level;
> > +	int cdclk, portclk;
> >  
> >  	/* 1. Enable DPLL power in DPLL_ENABLE. */
> >  	val = I915_READ(CNL_DPLL_ENABLE(pll->id));
> > @@ -2006,11 +2019,9 @@ static void cnl_ddi_pll_enable(struct drm_i915_private *dev_priv,
> >  	/*
> >  	 * 5. If the frequency will result in a change to the voltage
> >  	 * requirement, follow the Display Voltage Frequency Switching
> > -	 * Sequence Before Frequency Change
> > -	 *
> > -	 * FIXME: (DVFS) is used to adjust the display voltage to match the
> > -	 * display clock frequencies
> > +	 * (DVFS) Sequence Before Frequency Change
> >  	 */
> > +	ret = cnl_dvfs_pre_change(dev_priv);
> >  
> >  	/* 6. Enable DPLL in DPLL_ENABLE. */
> >  	val = I915_READ(CNL_DPLL_ENABLE(pll->id));
> > @@ -2028,11 +2039,14 @@ static void cnl_ddi_pll_enable(struct drm_i915_private *dev_priv,
> >  	/*
> >  	 * 8. If the frequency will result in a change to the voltage
> >  	 * requirement, follow the Display Voltage Frequency Switching
> > -	 * Sequence After Frequency Change
> > -	 *
> > -	 * FIXME: (DVFS) is used to adjust the display voltage to match the
> > -	 * display clock frequencies
> > +	 * (DVFS) Sequence After Frequency Change
> >  	 */
> > +	if (ret == 0) {
> > +		cdclk = dev_priv->cdclk.hw.cdclk;
> > +		portclk = intel_ddi_port_clock(dev_priv, pll->id);
> > +		level = cnl_get_dvfs_level(cdclk, portclk);
> > +		cnl_dvfs_post_change(dev_priv, level);
> 
> This isn't how I imagined we'd handle this. What I was after is
> pre-computing the correct "dfvfs level" (or what I'd probably just call
> "voltage" or something like that), and then we'd just let the normal
> cdclk programming sequence do its thing.
> 
> Is it even safe to do this with other pipes/ports enabled? I would
> have assumed no, but maybe I'm mistaken?

Well, this is how the spec is written. So I assume it is safe to change
that at that point.

Also we enable CDCLK during boot while we have no way to compute the
link rate. So I don't see a better way of hadling that.

So, Art is it ok in the way that I'm proposing here:

on core display init:

- dvfs-pre;
- enable cdclk;
- dvfs-post considering cdclk only and link rate 0; 

on pll init:

- consider cdclk and link rate and if desired level is different from what is currently set: dvfs-pre
- enable pll
- consider cdclk and link rate and if desired level is different from what is currently set: dvfs-post with new level.

This is how I read the spec, but please let me know what I'm missing.

Maybe I'm missing the link rate for eDP during core display init like we are currently kind of missing for SKL?

> 
> 
> > +	}
> >  
> >  	/*
> >  	 * 9. turn on the clock for the DDI and map the DPLL to the DDI
> > -- 
> > 2.13.5
> 
> -- 
> Ville Syrjälä
> Intel OTC