drm/i915: Sanitize PCH port transcoder select on IBX

IBX has a documented workaround which states that when we disable the
port we must change its transcoder select to A, otherwise it will
prevent the other port (DP vs. HDMI/SDVO) from using transcoder A.
We implement the workaround during encoder disable, but looks like
some BIOSen leave transcoder B selected even when the port wasn't
actually enabled by the BIOS. That will trip up our asserts
that attempt to make sure we never forget this w/a.

Sanitize the transcoder select to A for all disabled PCH
DP/HDMI/SDVO ports. We assume that the port was never enabled
by the BIOS on transcoder B, because if it had we'd actually have
to toggle the port on and back off to properly switch it back to
transcoder A. That would cause some display flicker if transcoder A
is already enabled on some other port, so it's better not to do it
unless absolutely necessary. Since we have no indication that the
transcoder select is misbehaving on the affected machines we can
assume the port was never actually enabled by the BIOS.

This cures warning like this during driver load:
IBX PCH DP C still using transcoder B
WARNING: CPU: 2 PID: 172 at drivers/gpu/drm/i915/intel_display.c:1279 assert_pch_dp_disabled+0x9e/0xb0 [i915]

v2: Add comments to remind the reader that SDVOB==HDMIB (Chris)

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181108143635.9556-1-ville.syrjala@linux.intel.comReviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_display.c

@@ -1316,6 +1316,7 @@ static void assert_pch_ports_disabled(struct drm_i915_private *dev_priv,
 			"PCH LVDS enabled on transcoder %c, should be disabled\n",
 			pipe_name(pipe));
 
+	/* PCH SDVOB multiplex with HDMIB */
 	assert_pch_hdmi_disabled(dev_priv, pipe, PORT_B, PCH_HDMIB);
 	assert_pch_hdmi_disabled(dev_priv, pipe, PORT_C, PCH_HDMIC);
 	assert_pch_hdmi_disabled(dev_priv, pipe, PORT_D, PCH_HDMID);
@@ -15655,6 +15656,65 @@ static void intel_early_display_was(struct drm_i915_private *dev_priv)
 	}
 }
 
+static void ibx_sanitize_pch_hdmi_port(struct drm_i915_private *dev_priv,
+				       enum port port, i915_reg_t hdmi_reg)
+{
+	u32 val = I915_READ(hdmi_reg);
+
+	if (val & SDVO_ENABLE ||
+	    (val & SDVO_PIPE_SEL_MASK) == SDVO_PIPE_SEL(PIPE_A))
+		return;
+
+	DRM_DEBUG_KMS("Sanitizing transcoder select for HDMI %c\n",
+		      port_name(port));
+
+	val &= ~SDVO_PIPE_SEL_MASK;
+	val |= SDVO_PIPE_SEL(PIPE_A);
+
+	I915_WRITE(hdmi_reg, val);
+}
+
+static void ibx_sanitize_pch_dp_port(struct drm_i915_private *dev_priv,
+				     enum port port, i915_reg_t dp_reg)
+{
+	u32 val = I915_READ(dp_reg);
+
+	if (val & DP_PORT_EN ||
+	    (val & DP_PIPE_SEL_MASK) == DP_PIPE_SEL(PIPE_A))
+		return;
+
+	DRM_DEBUG_KMS("Sanitizing transcoder select for DP %c\n",
+		      port_name(port));
+
+	val &= ~DP_PIPE_SEL_MASK;
+	val |= DP_PIPE_SEL(PIPE_A);
+
+	I915_WRITE(dp_reg, val);
+}
+
+static void ibx_sanitize_pch_ports(struct drm_i915_private *dev_priv)
+{
+	/*
+	 * The BIOS may select transcoder B on some of the PCH
+	 * ports even it doesn't enable the port. This would trip
+	 * assert_pch_dp_disabled() and assert_pch_hdmi_disabled().
+	 * Sanitize the transcoder select bits to prevent that. We
+	 * assume that the BIOS never actually enabled the port,
+	 * because if it did we'd actually have to toggle the port
+	 * on and back off to make the transcoder A select stick
+	 * (see. intel_dp_link_down(), intel_disable_hdmi(),
+	 * intel_disable_sdvo()).
+	 */
+	ibx_sanitize_pch_dp_port(dev_priv, PORT_B, PCH_DP_B);
+	ibx_sanitize_pch_dp_port(dev_priv, PORT_C, PCH_DP_C);
+	ibx_sanitize_pch_dp_port(dev_priv, PORT_D, PCH_DP_D);
+
+	/* PCH SDVOB multiplex with HDMIB */
+	ibx_sanitize_pch_hdmi_port(dev_priv, PORT_B, PCH_HDMIB);
+	ibx_sanitize_pch_hdmi_port(dev_priv, PORT_C, PCH_HDMIC);
+	ibx_sanitize_pch_hdmi_port(dev_priv, PORT_D, PCH_HDMID);
+}
+
 /* Scan out the current hw modeset state,
  * and sanitizes it to the current state
  */
@@ -15676,6 +15736,9 @@ intel_modeset_setup_hw_state(struct drm_device *dev,
 	/* HW state is read out, now we need to sanitize this mess. */
 	get_encoder_power_domains(dev_priv);
 
+	if (HAS_PCH_IBX(dev_priv))
+		ibx_sanitize_pch_ports(dev_priv);
+
 	/*
 	 * intel_sanitize_plane_mapping() may need to do vblank
 	 * waits, so we need vblank interrupts restored beforehand.