Re: [PATCH 1/2] drm/i915/display: Do both crawl and squash when changing cdclk

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> -----Original Message-----
> From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Sent: Thursday, October 20, 2022 8:15 AM
> To: Vivekanandan, Balasubramani
> <balasubramani.vivekanandan@xxxxxxxxx>
> Cc: Srivatsa, Anusha <anusha.srivatsa@xxxxxxxxx>; intel-
> gfx@xxxxxxxxxxxxxxxxxxxxx
> Subject: Re:  [PATCH 1/2] drm/i915/display: Do both crawl and
> squash when changing cdclk
> 
> On Thu, Oct 20, 2022 at 08:12:04PM +0530, Balasubramani Vivekanandan
> wrote:
> > On 13.10.2022 16:32, Anusha Srivatsa wrote:
> > > From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> > >
> > > For MTL, changing cdclk from between certain frequencies has both
> > > squash and crawl. Use the current cdclk config and the new(desired)
> > > cdclk config to construtc a mid cdclk config.
> > > Set the cdclk twice:
> > > - Current cdclk -> mid cdclk
> > > - mid cdclk -> desired cdclk
> > >
> > > v2: Add check in intel_modeset_calc_cdclk() to avoid cdclk change
> > > via modeset for platforms that support squash_crawl sequences(Ville)
> > >
> > > v3: Add checks for:
> > > - scenario where only slow clock is used and cdclk is actually 0
> > > (bringing up display).
> > > - PLLs are on before looking up the waveform.
> > > - Squash and crawl capability checks.(Ville)
> > >
> > > Signed-off-by: Anusha Srivatsa <anusha.srivatsa@xxxxxxxxx>
> > > Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> >
> > Please add the Bspec number.
> >
> > > ---
> > >  drivers/gpu/drm/i915/display/intel_cdclk.c | 157
> > > +++++++++++++++++----
> > >  1 file changed, 128 insertions(+), 29 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c
> > > b/drivers/gpu/drm/i915/display/intel_cdclk.c
> > > index ad401357ab66..430b4cb0a8ab 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_cdclk.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
> > > @@ -1675,7 +1675,7 @@ static u32 cdclk_squash_waveform(struct
> drm_i915_private *dev_priv,
> > >  	const struct intel_cdclk_vals *table = dev_priv->display.cdclk.table;
> > >  	int i;
> > >
> > > -	if (cdclk == dev_priv->display.cdclk.hw.bypass)
> > > +	if (cdclk == dev_priv->display.cdclk.hw.bypass || cdclk == 0)
> > >  		return 0;
> > >
> > >  	for (i = 0; table[i].refclk; i++)
> > > @@ -1689,37 +1689,72 @@ static u32 cdclk_squash_waveform(struct
> drm_i915_private *dev_priv,
> > >  	return 0xffff;
> > >  }
> > >
> > > -static void bxt_set_cdclk(struct drm_i915_private *dev_priv,
> > > -			  const struct intel_cdclk_config *cdclk_config,
> > > -			  enum pipe pipe)
> > > +static int cdclk_squash_divider(u16 waveform) {
> > > +	return hweight16(waveform ?: 0xffff); }
> > > +
> > > +static bool cdclk_crawl_and_squash(struct drm_i915_private *i915,
> > > +				   const struct intel_cdclk_config
> *old_cdclk_config,
> > > +				   const struct intel_cdclk_config
> *new_cdclk_config,
> > > +				   struct intel_cdclk_config *mid_cdclk_config)
> {
> >
> > I was thinking of asking to rename this function to a more descriptive
> > one, but then I myself was not able to come up with one.
> > For a fresh eyes, it is difficult to make out what this function is
> > actually doing.  Can you please add a summary as a comment above this
> > function pointing out what is mid_cdclk and whats the meaning of its
> > return value.
> >
> > > +	u16 old_waveform = cdclk_squash_waveform(i915, old_cdclk_config-
> >cdclk);
> > > +	u16 new_waveform = cdclk_squash_waveform(i915,
> new_cdclk_config->cdclk);
> > > +	u16 mid_waveform;
> > > +	int size = 16;
> > > +	int div = 2;
> > > +
> > > +	/* Return if both Squash and Crawl are not present */
> > > +	if (!HAS_CDCLK_CRAWL(i915) || !has_cdclk_squasher(i915))
> > > +		return false;
> >
> > Can cdclk_squasher feature availability be also made a part of
> > device_info structure like cdclk_crawl and create a macro similar to
> > HAS_CDCLK_CRAWL?
> > Like Ville said it looks bit weird. Also we would avoid adding
> > platform checks inside has_cdclk_squasher() function like it is done
> > now in your second patch.
> >
> > > +
> > > +	/* Return if Squash only or Crawl only is the desired action */
> > > +	if (old_cdclk_config->vco <= 0 || new_cdclk_config->vco <= 0 ||
> > > +	    old_cdclk_config->vco == new_cdclk_config->vco ||
> > > +	    old_waveform == new_waveform)
> > > +		return false;
> > > +
> > > +	*mid_cdclk_config = *new_cdclk_config;
> > > +
> > > +	/* If moving to a higher cdclk(squash) the mid cdclk config
> > > +	 * should have the new (squash) waveform.
> > > +	 * If moving to a lower cdclk (crawl) the mid cdclk config
> > > +	 * should have the new vco.
> > > +	 */
> > > +
> > > +	if (cdclk_squash_divider(new_waveform) >
> cdclk_squash_divider(old_waveform)) {
> > > +		mid_cdclk_config->vco = old_cdclk_config->vco;
> > > +		mid_waveform = new_waveform;
> > > +	} else {
> > > +		mid_cdclk_config->vco = new_cdclk_config->vco;
> > > +		mid_waveform = old_waveform;
> > > +	}
> > > +
> > > +	mid_cdclk_config->cdclk =
> DIV_ROUND_CLOSEST(cdclk_squash_divider(mid_waveform) *
> > > +						    mid_cdclk_config->vco, size
> * div);
> > > +
> > > +	/* make sure the mid clock came out sane */
> > > +
> > > +	drm_WARN_ON(&i915->drm, mid_cdclk_config->cdclk <
> > > +		    min(old_cdclk_config->cdclk, new_cdclk_config->cdclk));
> > > +	drm_WARN_ON(&i915->drm, mid_cdclk_config->cdclk >
> > > +		    i915->display.cdclk.max_cdclk_freq);
> > > +	drm_WARN_ON(&i915->drm, cdclk_squash_waveform(i915,
> mid_cdclk_config->cdclk) !=
> > > +		    mid_waveform);
> > > +
> > > +	return true;
> > > +}
> > > +
> > > +static void _bxt_set_cdclk(struct drm_i915_private *dev_priv,
> > > +			   const struct intel_cdclk_config *cdclk_config,
> > > +			   enum pipe pipe)
> > >  {
> > >  	int cdclk = cdclk_config->cdclk;
> > >  	int vco = cdclk_config->vco;
> > >  	u32 val;
> > >  	u16 waveform;
> > >  	int clock;
> > > -	int ret;
> > > -
> > > -	/* Inform power controller of upcoming frequency change. */
> > > -	if (DISPLAY_VER(dev_priv) >= 11)
> > > -		ret = skl_pcode_request(&dev_priv->uncore,
> SKL_PCODE_CDCLK_CONTROL,
> > > -					SKL_CDCLK_PREPARE_FOR_CHANGE,
> > > -					SKL_CDCLK_READY_FOR_CHANGE,
> > > -					SKL_CDCLK_READY_FOR_CHANGE, 3);
> > > -	else
> > > -		/*
> > > -		 * BSpec requires us to wait up to 150usec, but that leads to
> > > -		 * timeouts; the 2ms used here is based on experiment.
> > > -		 */
> > > -		ret = snb_pcode_write_timeout(&dev_priv->uncore,
> > > -
> HSW_PCODE_DE_WRITE_FREQ_REQ,
> > > -					      0x80000000, 150, 2);
> > > -	if (ret) {
> > > -		drm_err(&dev_priv->drm,
> > > -			"Failed to inform PCU about cdclk change (err %d,
> freq %d)\n",
> > > -			ret, cdclk);
> > > -		return;
> > > -	}
> > >
> > >  	if (HAS_CDCLK_CRAWL(dev_priv) && dev_priv->display.cdclk.hw.vco
> > 0 && vco > 0) {
> > >  		if (dev_priv->display.cdclk.hw.vco != vco) @@ -1772,6
> +1807,44 @@
> > > static void bxt_set_cdclk(struct drm_i915_private *dev_priv,
> > >
> > >  	if (pipe != INVALID_PIPE)
> > >
> 	intel_crtc_wait_for_next_vblank(intel_crtc_for_pipe(dev_priv,
> > > pipe));
> > > +}
> > > +
> > > +static void bxt_set_cdclk(struct drm_i915_private *dev_priv,
> > > +			  const struct intel_cdclk_config *cdclk_config,
> > > +			  enum pipe pipe)
> > > +{
> >
> > bxt_set_cdclk() is now bloated as it is reused for new platforms with
> > new features resulting in too many condition checks. I see it is now
> > time to switch to a new set_cdclk() function. I would prefer a new
> > function for platforms starting from which supports squash/crawl
> > feature and add this new crawl_and_squash feature implementation to
> > the same function. But definitely I dislike using bxt_set_cdclk for MTL.
> 
> bxt vs. icl split might make sense since there are a bunch of if-else along
> those lines. Beyond that it all we'd achieve is code duplication I think.
> 
> Well, we might be able to avoid some code duplication if we managed to
> chunk the different parts of bxt_set_cdclk() into lower level subfunctions,
> and just cobble together higher level variants (crawl+squash,just crawl,just
> squash, neither). But basically all of those are just subsets of the
> crawl+squash version, hence the duplication.

I agree.

> Another approach I was musing about was to add vfuncs for lower level
> operations (pll enable, pll disable, etc.) to get rid of the if-else stuff. But
> dunno if enough of the platforms would fit that model to make it sensible.

I will have to explore this myself.

> >
> > > +	struct intel_cdclk_config mid_cdclk_config;
> > > +	int cdclk = cdclk_config->cdclk;
> > > +	int ret;
> > > +
> > > +	/* Inform power controller of upcoming frequency change. */
> > > +	if (DISPLAY_VER(dev_priv) >= 11)
> > > +		ret = skl_pcode_request(&dev_priv->uncore,
> SKL_PCODE_CDCLK_CONTROL,
> > > +					SKL_CDCLK_PREPARE_FOR_CHANGE,
> > > +					SKL_CDCLK_READY_FOR_CHANGE,
> > > +					SKL_CDCLK_READY_FOR_CHANGE, 3);
> > > +	else
> > > +		/*
> > > +		 * BSpec requires us to wait up to 150usec, but that leads to
> > > +		 * timeouts; the 2ms used here is based on experiment.
> > > +		 */
> > > +		ret = snb_pcode_write_timeout(&dev_priv->uncore,
> > > +
> HSW_PCODE_DE_WRITE_FREQ_REQ,
> > > +					      0x80000000, 150, 2);
> > > +	if (ret) {
> > > +		drm_err(&dev_priv->drm,
> > > +			"Failed to inform PCU about cdclk change (err %d,
> freq %d)\n",
> > > +			ret, cdclk);
> > > +		return;
> > > +	}
> > > +
> > > +	if (cdclk_crawl_and_squash(dev_priv, &dev_priv->display.cdclk.hw,
> > > +				   cdclk_config, &mid_cdclk_config)) {
> > > +		_bxt_set_cdclk(dev_priv, &mid_cdclk_config, pipe);
> > > +		_bxt_set_cdclk(dev_priv, cdclk_config, pipe);
> > > +	} else {
> > > +		_bxt_set_cdclk(dev_priv, cdclk_config, pipe);
> > > +	}
> > >
> > >  	if (DISPLAY_VER(dev_priv) >= 11) {
> > >  		ret = snb_pcode_write(&dev_priv->uncore,
> SKL_PCODE_CDCLK_CONTROL,
> > > @@ -1944,6 +2017,27 @@ void intel_cdclk_uninit_hw(struct
> drm_i915_private *i915)
> > >  		skl_cdclk_uninit_hw(i915);
> > >  }
> > >
> > > +static bool intel_cdclk_can_crawl_and_squash(struct drm_i915_private
> *i915,
> > > +					     const struct intel_cdclk_config *a,
> > > +					     const struct intel_cdclk_config *b) {
> > > +	u16 old_waveform;
> > > +	u16 new_waveform;
> > > +
> > > +	if (a->vco == 0 || b->vco == 0)
> > > +		return false;
> > > +
> > > +	if (HAS_CDCLK_CRAWL(i915) && has_cdclk_squasher(i915)) {
> > > +		old_waveform = cdclk_squash_waveform(i915, a->cdclk);
> > > +		new_waveform = cdclk_squash_waveform(i915, b->cdclk);
> > > +	} else {
> > > +		return false;
> > > +	}
> > > +
> > > +	return a->vco != b->vco &&
> > > +	       old_waveform != new_waveform; }
> > > +
> > >  static bool intel_cdclk_can_crawl(struct drm_i915_private *dev_priv,
> > >  				  const struct intel_cdclk_config *a,
> > >  				  const struct intel_cdclk_config *b) @@ -
> 2750,9 +2844,14 @@
> > > int intel_modeset_calc_cdclk(struct intel_atomic_state *state)
> > >  			pipe = INVALID_PIPE;
> > >  	}
> > >
> > > -	if (intel_cdclk_can_squash(dev_priv,
> > > -				   &old_cdclk_state->actual,
> > > -				   &new_cdclk_state->actual)) {
> > > +	if (intel_cdclk_can_crawl_and_squash(dev_priv,
> > > +					     &old_cdclk_state->actual,
> > > +					     &new_cdclk_state->actual)) {
> > > +		drm_dbg_kms(&dev_priv->drm,
> > > +			    "Can change cdclk via crawler and squasher\n");
> > > +	} else if (intel_cdclk_can_squash(dev_priv,
> > > +					&old_cdclk_state->actual,
> > > +					&new_cdclk_state->actual)) {
> >
> > In the bxt_set_cdclk(), we perform crawl_and_squash only if neither
> > crawl and squash alone can't accomplish cdclk change. So move the
> > intel_cdclk_can_crawl_and_squash() check to after the checks for crawl
> > and squash individually.
> > This would just make sure the logs reflect how actually the cdclk is
> > changed.
> 
> The current order seems fine to me. intel_cdclk_can_crawl_and_squash()
> shouldn't say yes unless both crawl and squash are needed.
 Agreed here.

Anusha
> >
> > Regards,
> > Bala
> >
> > >  		drm_dbg_kms(&dev_priv->drm,
> > >  			    "Can change cdclk via squasher\n");
> > >  	} else if (intel_cdclk_can_crawl(dev_priv,
> > > --
> > > 2.25.1
> > >
> 
> --
> Ville Syrjälä
> Intel




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