drm/i915: disable LVDS downclock by default
Many platform support this feature, and it can provide significant
power savings when the reduced refresh rate is low. However, on some
platforms a secondary (reduced) timing is provided but not actually
supported by the hardware. This results in undesirable flicker at
runtime.
So disable the feature by default, but allow users to opt-in to the
reduced clock behavior with a new module parameter, lvds_downclock,
that can be set to 1 to enable the feature.
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>
diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 66f7bac..46d8896 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -45,6 +45,9 @@
unsigned int i915_powersave = 1;
module_param_named(powersave, i915_powersave, int, 0400);
+unsigned int i915_lvds_downclock = 0;
+module_param_named(lvds_downclock, i915_lvds_downclock, int, 0400);
+
static struct drm_driver driver;
#define INTEL_VGA_DEVICE(id, info) { \
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 445c49c..5f781a7 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -722,6 +722,7 @@
extern int i915_max_ioctl;
extern unsigned int i915_fbpercrtc;
extern unsigned int i915_powersave;
+extern unsigned int i915_lvds_downclock;
extern void i915_save_display(struct drm_device *dev);
extern void i915_restore_display(struct drm_device *dev);
diff --git a/drivers/gpu/drm/i915/intel_bios.c b/drivers/gpu/drm/i915/intel_bios.c
index f275677..b53c46f 100644
--- a/drivers/gpu/drm/i915/intel_bios.c
+++ b/drivers/gpu/drm/i915/intel_bios.c
@@ -197,7 +197,8 @@
memset(temp_mode, 0, sizeof(*temp_mode));
}
kfree(temp_mode);
- if (temp_downclock < panel_fixed_mode->clock) {
+ if (temp_downclock < panel_fixed_mode->clock &&
+ i915_lvds_downclock) {
dev_priv->lvds_downclock_avail = 1;
dev_priv->lvds_downclock = temp_downclock;
DRM_DEBUG_KMS("LVDS downclock is found in VBT. ",
diff --git a/drivers/gpu/drm/i915/intel_lvds.c b/drivers/gpu/drm/i915/intel_lvds.c
index 5041590..aa74e59 100644
--- a/drivers/gpu/drm/i915/intel_lvds.c
+++ b/drivers/gpu/drm/i915/intel_lvds.c
@@ -926,7 +926,8 @@
}
}
mutex_unlock(&dev->mode_config.mutex);
- if (temp_downclock < panel_fixed_mode->clock) {
+ if (temp_downclock < panel_fixed_mode->clock &&
+ i915_lvds_downclock) {
/* We found the downclock for LVDS. */
dev_priv->lvds_downclock_avail = 1;
dev_priv->lvds_downclock = temp_downclock;