[Intel-gfx] [PATCH] drm/i915/glk, cnl: Implement WaDisableScalarClockGating

[Imre Deak]

On GLK and CNL enabling a pipe with its pipe scaler enabled will result
in a FIFO underrun. This happens only once after driver loading or
system/runtime resume, more specifically after power well 1 gets
enabled; subsequent modesets seem to be free of underruns. The BSpec
workaround for this is to disable the pipe scaler clock gating for the
duration of modeset. Based on my tests disabling clock gating must be
done before enabling pipe scaling and we can re-enable it after the pipe
is enabled and one vblank has passed.

For consistency I also checked if plane scaling would cause the same
problem, but that doesn't seem to trigger this problem.

The patch is based on an earlier version from Ander.

Cc: Ander Conselvan de Oliveira <conselvan2 at gmail.com>
Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100302
Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/i915/i915_reg.h      |  8 ++++++++
 drivers/gpu/drm/i915/intel_display.c | 25 +++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 82f36dd0cd94..40a3c045d9d0 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -3811,6 +3811,14 @@ enum {
 #define   PWM2_GATING_DIS		(1 << 14)
 #define   PWM1_GATING_DIS		(1 << 13)
 
+#define _CLKGATE_DIS_PSL_A		0x46520
+#define _CLKGATE_DIS_PSL_B		0x46524
+#define _CLKGATE_DIS_PSL_C		0x46528
+#define   DPF_GATING_DIS		(1 << 10)
+
+#define CLKGATE_DIS_PSL(pipe) \
+	_MMIO_PIPE(pipe, _CLKGATE_DIS_PSL_A, _CLKGATE_DIS_PSL_B)
+
 /*
  * GEN10 clock gating regs
  */
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 026fa5460fe5..9d0b5a5596a5 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -5459,6 +5459,19 @@ static bool hsw_crtc_supports_ips(struct intel_crtc *crtc)
 	return HAS_IPS(to_i915(crtc->base.dev)) && crtc->pipe == PIPE_A;
 }
 
+static void glk_pipe_scaler_clock_gating_wa(struct drm_i915_private *dev_priv,
+					    enum pipe pipe, bool apply)
+{
+	u32 tmp = I915_READ(CLKGATE_DIS_PSL(pipe));
+
+	if (apply)
+		tmp |= DPF_GATING_DIS;
+	else
+		tmp &= ~DPF_GATING_DIS;
+
+	I915_WRITE(CLKGATE_DIS_PSL(pipe), tmp);
+}
+
 static void haswell_crtc_enable(struct intel_crtc_state *pipe_config,
 				struct drm_atomic_state *old_state)
 {
@@ -5469,6 +5482,7 @@ static void haswell_crtc_enable(struct intel_crtc_state *pipe_config,
 	enum transcoder cpu_transcoder = intel_crtc->config->cpu_transcoder;
 	struct intel_atomic_state *old_intel_state =
 		to_intel_atomic_state(old_state);
+	bool psl_clkgate_wa;
 
 	if (WARN_ON(intel_crtc->active))
 		return;
@@ -5522,6 +5536,12 @@ static void haswell_crtc_enable(struct intel_crtc_state *pipe_config,
 	if (!transcoder_is_dsi(cpu_transcoder))
 		intel_ddi_enable_pipe_clock(pipe_config);
 
+	/* WaDisableScalarClockGating: glk, cnl */
+	psl_clkgate_wa = (IS_GEMINILAKE(dev_priv) || IS_CANNONLAKE(dev_priv)) &&
+			 intel_crtc->config->pch_pfit.enabled;
+	if (psl_clkgate_wa)
+		glk_pipe_scaler_clock_gating_wa(dev_priv, pipe, true);
+
 	if (INTEL_GEN(dev_priv) >= 9)
 		skylake_pfit_enable(intel_crtc);
 	else
@@ -5555,6 +5575,11 @@ static void haswell_crtc_enable(struct intel_crtc_state *pipe_config,
 
 	intel_encoders_enable(crtc, pipe_config, old_state);
 
+	if (psl_clkgate_wa) {
+		intel_wait_for_vblank(dev_priv, pipe);
+		glk_pipe_scaler_clock_gating_wa(dev_priv, pipe, false);
+	}
+
 	if (intel_crtc->config->has_pch_encoder) {
 		intel_wait_for_vblank(dev_priv, pipe);
 		intel_wait_for_vblank(dev_priv, pipe);
-- 
2.13.2