[Intel-gfx] [PATCH v2 2/2] drm/i915/intel_dsi: Read back pclk set by GOP and use that as pclk v2

[Hans de Goede]

On BYT and CHT the GOP sometimes initializes the pclk at a (slightly)
different frequency then the pclk which we've calculated.

This commit makes the DSI code read-back the pclk set by the GOP and
if that is within a reasonable margin of the calculated pclk, uses
that instead.

This fixes the first modeset being a full modeset instead of a
fast modeset on systems where the GOP pclk is different.

Changes in v2:
-Use intel_encoder_current_mode() to get the pclk setup by the GOP

Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/gpu/drm/i915/intel_dsi_vbt.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_dsi_vbt.c b/drivers/gpu/drm/i915/intel_dsi_vbt.c
index ac83d6b89ae0..3387b187105c 100644
--- a/drivers/gpu/drm/i915/intel_dsi_vbt.c
+++ b/drivers/gpu/drm/i915/intel_dsi_vbt.c
@@ -506,6 +506,7 @@ bool intel_dsi_vbt_init(struct intel_dsi *intel_dsi, u16 panel_id)
 	struct mipi_config *mipi_config = dev_priv->vbt.dsi.config;
 	struct mipi_pps_data *pps = dev_priv->vbt.dsi.pps;
 	struct drm_display_mode *mode = dev_priv->vbt.lfp_lvds_vbt_mode;
+	struct drm_display_mode *curr;
 	u32 bpp;
 	u32 tlpx_ns, extra_byte_count, bitrate, tlpx_ui;
 	u32 ui_num, ui_den;
@@ -583,6 +584,23 @@ bool intel_dsi_vbt_init(struct intel_dsi *intel_dsi, u16 panel_id)
 	} else
 		burst_mode_ratio = 100;
 
+	/*
+	 * On BYT / CRC the GOP sometimes picks a slightly different pclk,
+	 * read back the GOP configured pclk and prefer it over ours.
+	 */
+	if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv)) {
+		curr = intel_encoder_current_mode(&intel_dsi->base);
+		if (curr) {
+			DRM_DEBUG_KMS("Calculated pclk %d GOP %d\n",
+				      pclk, curr->clock);
+			if (curr->clock >= (pclk * 9 / 10) &&
+			    curr->clock <= (pclk * 11 / 10))
+				pclk = curr->clock;
+
+			kfree(curr);
+		}
+	}
+
 	intel_dsi->burst_mode_ratio = burst_mode_ratio;
 	intel_dsi->pclk = pclk;
 
-- 
2.19.0