[Intel-gfx] [PATCH] drm/i915/tgl: Lower cdclk for sub 4k resolutions

[Shankar, Uma]

>-----Original Message-----
>From: Kahola, Mika
>Sent: Tuesday, August 20, 2019 4:37 PM
>To: intel-gfx at lists.freedesktop.org
>Cc: Shankar, Uma <uma.shankar at intel.com>; Kahola, Mika
><mika.kahola at intel.com>
>Subject: [PATCH] drm/i915/tgl: Lower cdclk for sub 4k resolutions
>
>In order to achieve improved power savings we can tune down CD clock frequency for
>sub 4k resolutions. The maximum CD clock frequency for sub 4k resolutions is set to
>172.8 MHz.
>
>Signed-off-by: Mika Kahola <mika.kahola at intel.com>
>---
> drivers/gpu/drm/i915/display/intel_cdclk.c | 26 +++++++++++++++++++++-
>drivers/gpu/drm/i915/display/intel_cdclk.h |  3 +++
> 2 files changed, 28 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c
>b/drivers/gpu/drm/i915/display/intel_cdclk.c
>index d0bc42e5039c..1d6c7bc79470 100644
>--- a/drivers/gpu/drm/i915/display/intel_cdclk.c
>+++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
>@@ -2610,6 +2610,24 @@ static int intel_compute_max_dotclk(struct
>drm_i915_private *dev_priv)
> 		return max_cdclk_freq*90/100;
> }
>
>+bool mode_is_4k(struct drm_i915_private *dev_priv) {
>+	struct intel_crtc *crtc;
>+	struct intel_crtc_state *pipe_config;
>+
>+	for_each_intel_crtc(&dev_priv->drm, crtc) {
>+		pipe_config = to_intel_crtc_state(crtc->base.state);
>+
>+		if (pipe_config->base.active) {
>+			if (pipe_config->pipe_src_w >= WIDTH_4K &&
>+			    pipe_config->pipe_src_h >= HEIGHT_4K)
>+				return true;
>+		}
>+	}
>+
>+	return false;
>+}
>+
> /**
>  * intel_update_max_cdclk - Determine the maximum support CDCLK frequency
>  * @dev_priv: i915 device
>@@ -2620,7 +2638,13 @@ static int intel_compute_max_dotclk(struct
>drm_i915_private *dev_priv)
>  */
> void intel_update_max_cdclk(struct drm_i915_private *dev_priv)  {
>-	if (IS_ELKHARTLAKE(dev_priv)) {
>+	/*
>+	 * Use lower CDCLK frequency on Tigerlake when selected
>+	 * mode is less than 4k.
>+	 */
>+	if (INTEL_GEN(dev_priv) >= 12 && !mode_is_4k(dev_priv)) {
>+		dev_priv->max_cdclk_freq = 172800;
>+	} else if (IS_ELKHARTLAKE(dev_priv)) {

Setting the max cd clock supported itself to a lower value is not a good idea.
This should return what is the max frequency of cd clock the hardware supports.
Driver is not going to program this to max based on this data.

Actual cd clock which will be programmed in hardware should be based on the
maximum pixel clock we are driving. So if we are not driving 4K and say at 1920x1080, pixel
clock will be less and we should be selecting a lower value of cd clock in that case which
gets programmed in CDCLK_CTL. But max cd clock still remains what maximum the platform can
support. You can check intel_compute_min_cdclk which calculates the minimum cd clock required.

So when we just have 1920x1080 at 60Hz pixel clock of 148500, 
min cd clock required should be 148500 and nearest higher value of CD Clock will be 172.8Mhz.
Similarly for 4096x2160 at 60, pixel clock 556188, min cd clock calculated will be 556.188 MHz, thus
getting nearest supported cd clock value of 556 or 648Mhz.

This should be taken care by this logic in driver. 

Also with the current patch, modes like 2560x1600 at 60, pixel clock 268.5MHz will not work. This will need
cd clock of 324Mhz (or 307, 312 whatever are supported on the platform. 

> 		if (dev_priv->cdclk.hw.ref == 24000)
> 			dev_priv->max_cdclk_freq = 552000;
> 		else
>diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.h
>b/drivers/gpu/drm/i915/display/intel_cdclk.h
>index 4d6f7f5f8930..cefb5146ddca 100644
>--- a/drivers/gpu/drm/i915/display/intel_cdclk.h
>+++ b/drivers/gpu/drm/i915/display/intel_cdclk.h
>@@ -15,6 +15,9 @@ struct intel_atomic_state;  struct intel_cdclk_state;  struct
>intel_crtc_state;
>
>+#define WIDTH_4K  3860
>+#define HEIGHT_4K 2160
>+
> int intel_crtc_compute_min_cdclk(const struct intel_crtc_state *crtc_state);  void
>intel_cdclk_init(struct drm_i915_private *i915);  void intel_cdclk_uninit(struct
>drm_i915_private *i915);
>--
>2.17.1