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

[Balasubramani Vivekanandan <balasubramani.vivekanandan@intel.com>]

On 13.10.2022 16:32, Anusha Srivatsa wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> 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@intel.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

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.

> +	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.

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
>