[Intel-gfx] [PATCH 2/2] drm/i915: Implement manual override of LVDS single/dual channel mode

[Chris Wilson]

From: Mike Isely <isely at isely.net>

The logic for LVDS setup in the Intel driver needs to know whether the
LVDS port should be in single or dual channel mode when calculating
video timing.  It had been answering this question by probing the
current hardware configuration, under the assumption that the video
BIOS would have already set it up.  But the video BIOS would actually
have to know how to set up the LVDS port for the connected device,
which is a bad assumption if the display device is not integral to the
processor board - a situation that can exist for embedded situation.
This is yet one more case where the Intel driver had been implicitly
relying on the video BIOS for display configuration.

This changes creates a new kernel option, lvds_channels, which can be
used to override the probe.  Setting this allows the user to specify
the number of channels in use, avoiding the possibly erroneous probe
of the hardware.  Almost nobody should ever need to touch this option,
and its default value of zero is interpreted to preserve existing
probe-the-hardware behavior.  But if the video BIOS gets this "wrong",
then it can be overridden by setting lvds_channels to 1 or 2,
indicating single or dual channel LVDS mode, respectively.

Signed-off-by: Mike Isely <isely at isely.net>
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_drv.c      |    4 ++++
 drivers/gpu/drm/i915/i915_drv.h      |    1 +
 drivers/gpu/drm/i915/intel_display.c |   32 +++++++++++++++++---------------
 3 files changed, 22 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 29ee1e3..16a2532 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -71,6 +71,10 @@ unsigned int i915_lvds_24bit = 0;
 module_param_named(lvds_24bit, i915_lvds_24bit, int, 0600);
 MODULE_PARM_DESC(lvds_24bit, "LVDS 24 bit pixel format: 0=leave untouched (default), 1=24 bit '2.0' format, 2=24 bit '2.1' format, 3=force older 18 bit format");
 
+unsigned int i915_lvds_channels = 0;
+module_param_named(lvds_channels, i915_lvds_channels, int, 0600);
+MODULE_PARM_DESC(lvds_channels, "LVDS channels in use: 0=(default) probe hardware 1=single 2=dual");
+
 static struct drm_driver driver;
 extern int intel_agp_enabled;
 
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 97153f0..2112af3 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -977,6 +977,7 @@ extern unsigned int i915_fbpercrtc;
 extern int i915_panel_ignore_lid;
 extern unsigned int i915_powersave;
 extern unsigned int i915_semaphores;
+extern unsigned int i915_lvds_channels;
 extern unsigned int i915_lvds_downclock;
 extern unsigned int i915_panel_use_ssc;
 extern int i915_vbt_sdvo_panel_type;
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index f84dd21..7734d1e 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -354,6 +354,17 @@ static const intel_limit_t intel_limits_ironlake_display_port = {
         .find_pll = intel_find_pll_ironlake_dp,
 };
 
+static bool intel_lvds_is_dual_channel_mode(struct drm_i915_private *dev_priv,
+					    int lvds_reg)
+{
+	/* Did the user specify the number of channels? */
+	if (i915_lvds_channels)
+		return i915_lvds_channels == 2;
+
+	/* No, let's probe the current status of the hardware instead. */
+	return (I915_READ(lvds_reg) & LVDS_CLKB_POWER_MASK) == LVDS_CLKB_POWER_UP;
+}
+
 static const intel_limit_t *intel_ironlake_limit(struct drm_crtc *crtc,
 						int refclk)
 {
@@ -362,8 +373,7 @@ static const intel_limit_t *intel_ironlake_limit(struct drm_crtc *crtc,
 	const intel_limit_t *limit;
 
 	if (intel_pipe_has_type(crtc, INTEL_OUTPUT_LVDS)) {
-		if ((I915_READ(PCH_LVDS) & LVDS_CLKB_POWER_MASK) ==
-		    LVDS_CLKB_POWER_UP) {
+		if (intel_lvds_is_dual_channel_mode(dev_priv, PCH_LVDS)) {
 			/* LVDS dual channel */
 			if (refclk == 100000)
 				limit = &intel_limits_ironlake_dual_lvds_100m;
@@ -391,8 +401,7 @@ static const intel_limit_t *intel_g4x_limit(struct drm_crtc *crtc)
 	const intel_limit_t *limit;
 
 	if (intel_pipe_has_type(crtc, INTEL_OUTPUT_LVDS)) {
-		if ((I915_READ(LVDS) & LVDS_CLKB_POWER_MASK) ==
-		    LVDS_CLKB_POWER_UP)
+		if (intel_lvds_is_dual_channel_mode(dev_priv, LVDS))
 			/* LVDS with dual channel */
 			limit = &intel_limits_g4x_dual_channel_lvds;
 		else
@@ -523,14 +532,7 @@ intel_find_best_PLL(const intel_limit_t *limit, struct drm_crtc *crtc,
 
 	if (intel_pipe_has_type(crtc, INTEL_OUTPUT_LVDS) &&
 	    (I915_READ(LVDS)) != 0) {
-		/*
-		 * For LVDS, if the panel is on, just rely on its current
-		 * settings for dual-channel.  We haven't figured out how to
-		 * reliably set up different single/dual channel state, if we
-		 * even can.
-		 */
-		if ((I915_READ(LVDS) & LVDS_CLKB_POWER_MASK) ==
-		    LVDS_CLKB_POWER_UP)
+		if (intel_lvds_is_dual_channel_mode(dev_priv, LVDS))
 			clock.p2 = limit->p2.p2_fast;
 		else
 			clock.p2 = limit->p2.p2_slow;
@@ -594,8 +596,8 @@ intel_g4x_find_best_PLL(const intel_limit_t *limit, struct drm_crtc *crtc,
 			lvds_reg = PCH_LVDS;
 		else
 			lvds_reg = LVDS;
-		if ((I915_READ(lvds_reg) & LVDS_CLKB_POWER_MASK) ==
-		    LVDS_CLKB_POWER_UP)
+
+		if (intel_lvds_is_dual_channel_mode(dev_priv, lvds_reg))
 			clock.p2 = limit->p2.p2_fast;
 		else
 			clock.p2 = limit->p2.p2_slow;
@@ -4914,7 +4916,7 @@ static int ironlake_crtc_mode_set(struct drm_crtc *crtc,
 	if (is_lvds) {
 		if ((intel_panel_use_ssc(dev_priv) &&
 		     dev_priv->lvds_ssc_freq == 100) ||
-		    (I915_READ(PCH_LVDS) & LVDS_CLKB_POWER_MASK) == LVDS_CLKB_POWER_UP)
+		    intel_lvds_is_dual_channel_mode(dev_priv, PCH_LVDS))
 			factor = 25;
 	} else if (is_sdvo && is_tv)
 		factor = 20;
-- 
1.7.4.1