[Intel-gfx] [PATCH] drm/i915/glk: CDCLK calculation changes for glk

[Madhav Chauhan]

As per BSPEC, valid cdclk values for glk are 79.2, 158.4, 316.8 Mhz.
Practically we can achive only 99% of these cdclk values(HW team
checking on this). So cdclk should be calculated for the given pixclk as
per that otherwise it may lead to screen corruption for some scenarios.

v2: Rebased to new CDLCK code framework
v3: Addressed review comments from Ander/Jani
    - Add comment in code about 99% usage of CDCLK
    - Calculate max dot clock as well with 99% limit

Signed-off-by: Madhav Chauhan <madhav.chauhan at intel.com>
---
 drivers/gpu/drm/i915/intel_cdclk.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_cdclk.c b/drivers/gpu/drm/i915/intel_cdclk.c
index c2cc33f..a661c7e 100644
--- a/drivers/gpu/drm/i915/intel_cdclk.c
+++ b/drivers/gpu/drm/i915/intel_cdclk.c
@@ -1071,9 +1071,13 @@ static int bxt_calc_cdclk(int max_pixclk)
 
 static int glk_calc_cdclk(int max_pixclk)
 {
-	if (max_pixclk > 2 * 158400)
+	/*
+	 * For GLK platform 316.8, 158.4, 79.2 MHz are the CDCLK values
+	 * as per BSPEC. But practically we can only achieve 99% of these.
+	 */
+	if (max_pixclk > DIV_ROUND_UP(2 * 158400 * 99, 100))
 		return 316800;
-	else if (max_pixclk > 2 * 79200)
+	else if (max_pixclk > DIV_ROUND_UP(2 * 79200 * 99, 100))
 		return 158400;
 	else
 		return 79200;
@@ -1613,7 +1617,6 @@ static int bxt_modeset_calc_cdclk(struct drm_atomic_state *state)
 		cdclk = bxt_calc_cdclk(max_pixclk);
 		vco = bxt_de_pll_vco(dev_priv, cdclk);
 	}
-
 	if (cdclk > dev_priv->max_cdclk_freq) {
 		DRM_DEBUG_KMS("requested cdclk (%d kHz) exceeds max (%d kHz)\n",
 			      cdclk, dev_priv->max_cdclk_freq);
@@ -1647,7 +1650,7 @@ static int intel_compute_max_dotclk(struct drm_i915_private *dev_priv)
 	int max_cdclk_freq = dev_priv->max_cdclk_freq;
 
 	if (IS_GEMINILAKE(dev_priv))
-		return 2 * max_cdclk_freq;
+		return 2 * max_cdclk_freq * 99/100;
 	else if (INTEL_INFO(dev_priv)->gen >= 9 ||
 		 IS_HASWELL(dev_priv) || IS_BROADWELL(dev_priv))
 		return max_cdclk_freq;
-- 
1.9.1