drm/i915: Program PFI credits for VLV

PFI credit programming is required when CD clock (related to data flow from
display pipeline to end display) is greater than CZ clock (related to data
flow from memory to display plane). This programming should be done when all
planes are OFF to avoid intermittent hangs while accessing memory even from
different Gfx units (not just display).

If cdclk/czclk >=1, PFI credits could be set as any number. To get better
performance, larger PFI credit can be assigned to PND. Otherwise if
cdclk/czclk<1, the default PFI credit of 8 should be set.

v2:
    - Change log to lower log level instead of DRM_ERROR
    - Change function name to valleyview_program_pfi_credits
    - Move program PFI credits to modeset_init instead of intel_set_mode
    - Change magic numbers to logical constants

[vsyrjala v3:
 - only program in response to cdclk update
 - program the credits also when cdclk<czclk
 - add CHV bits
 v4:
 - Change CHV cdclk<czclk credits to 12 (Vijay)]

Signed-off-by: Vidya Srinivas <vidya.srinivas@intel.com>
Signed-off-by: Gajanan Bhat <gajanan.bhat@intel.com>
Signed-off-by: Vandana Kannan <vandana.kannan@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Vijay Purushothaman <vijay.a.purushothaman@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -2105,6 +2105,14 @@ enum skl_disp_power_wells {
 #define   CDCLK_FREQ_SHIFT	4
 #define   CDCLK_FREQ_MASK	(0x1f << CDCLK_FREQ_SHIFT)
 #define   CZCLK_FREQ_MASK	0xf
+
+#define GCI_CONTROL		(VLV_DISPLAY_BASE + 0x650C)
+#define   PFI_CREDIT_63		(9 << 28)		/* chv only */
+#define   PFI_CREDIT_31		(8 << 28)		/* chv only */
+#define   PFI_CREDIT(x)		(((x) - 8) << 28)	/* 8-15 */
+#define   PFI_CREDIT_RESEND	(1 << 27)
+#define   VGA_FAST_MODE_DISABLE	(1 << 14)
+
 #define GMBUSFREQ_VLV		(VLV_DISPLAY_BASE + 0x6510)
 
 /*

drivers/gpu/drm/i915/intel_display.c

@@ -5100,6 +5100,42 @@ static void valleyview_modeset_global_pipes(struct drm_device *dev,
 			*prepare_pipes |= (1 << intel_crtc->pipe);
 }
 
+static void vlv_program_pfi_credits(struct drm_i915_private *dev_priv)
+{
+	unsigned int credits, default_credits;
+
+	if (IS_CHERRYVIEW(dev_priv))
+		default_credits = PFI_CREDIT(12);
+	else
+		default_credits = PFI_CREDIT(8);
+
+	if (DIV_ROUND_CLOSEST(dev_priv->vlv_cdclk_freq, 1000) >= dev_priv->rps.cz_freq) {
+		/* CHV suggested value is 31 or 63 */
+		if (IS_CHERRYVIEW(dev_priv))
+			credits = PFI_CREDIT_31;
+		else
+			credits = PFI_CREDIT(15);
+	} else {
+		credits = default_credits;
+	}
+
+	/*
+	 * WA - write default credits before re-programming
+	 * FIXME: should we also set the resend bit here?
+	 */
+	I915_WRITE(GCI_CONTROL, VGA_FAST_MODE_DISABLE |
+		   default_credits);
+
+	I915_WRITE(GCI_CONTROL, VGA_FAST_MODE_DISABLE |
+		   credits | PFI_CREDIT_RESEND);
+
+	/*
+	 * FIXME is this guaranteed to clear
+	 * immediately or should we poll for it?
+	 */
+	WARN_ON(I915_READ(GCI_CONTROL) & PFI_CREDIT_RESEND);
+}
+
 static void valleyview_modeset_global_resources(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -5123,6 +5159,8 @@ static void valleyview_modeset_global_resources(struct drm_device *dev)
 		else
 			valleyview_set_cdclk(dev, req_cdclk);
 
+		vlv_program_pfi_credits(dev_priv);
+
 		intel_display_power_put(dev_priv, POWER_DOMAIN_PIPE_A);
 	}
 }