[PATCH 4/4] drm/i915/intel_dsi: Read back pclk set by GOP and use that as pclk

[Hans de Goede <j.w.r.degoede@gmail.com>]

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.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
 drivers/gpu/drm/i915/intel_dsi_vbt.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_dsi_vbt.c b/drivers/gpu/drm/i915/intel_dsi_vbt.c
index 4d6ffa7b3e7b..d4cc6099012c 100644
--- a/drivers/gpu/drm/i915/intel_dsi_vbt.c
+++ b/drivers/gpu/drm/i915/intel_dsi_vbt.c
@@ -517,6 +517,7 @@ bool intel_dsi_vbt_init(struct intel_dsi *intel_dsi, u16 panel_id)
 	u32 mul;
 	u16 burst_mode_ratio;
 	enum port port;
+	enum pipe pipe;
 
 	DRM_DEBUG_KMS("\n");
 
@@ -583,6 +584,19 @@ 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)) &&
+	    intel_dsi_get_hw_state(&intel_dsi->base, &pipe)) {
+		u32 gop = intel_dsi_get_pclk(&intel_dsi->base, bpp, NULL);
+
+		DRM_DEBUG_KMS("Calculated pclk %d GOP %d\n", pclk, gop);
+		if (gop >= (pclk * 9 / 10) && gop <= (pclk * 11 / 10))
+			pclk = gop;
+	}
+
 	intel_dsi->burst_mode_ratio = burst_mode_ratio;
 	intel_dsi->pclk = pclk;
 
-- 
2.17.1

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