i915.enable_dithering allows to force dithering on all outputs on (=1) or off (=0). The default is -1 for current automatic per-pipe selection.
This is useful for debugging and for special case scenarios, e.g., providing simulated 10 bpc output on 8 bpc digital sinks if a 10 bpc framebuffer + rendering is in use.
A more flexible solution would be connector properties, like other drivers (radeon, amdgpu, nouveau) already provide. A global override via module parameter is useful even with such connector properties, e.g., for scientific applications which require strict control over dithering, to have an override for DE's which may not expose such properties via some standard protocol in a user-controllable way, e.g., afaik all currently existing Wayland compositors.
Tested on Ironlake, IvyBridge, Haswell, Skylake.
Signed-off-by: Mario Kleiner mario.kleiner.de@gmail.com --- drivers/gpu/drm/i915/i915_params.c | 5 +++++ drivers/gpu/drm/i915/i915_params.h | 1 + drivers/gpu/drm/i915/intel_display.c | 5 +++++ 3 files changed, 11 insertions(+)
diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c index 8ab003dca113..07ec3a96457c 100644 --- a/drivers/gpu/drm/i915/i915_params.c +++ b/drivers/gpu/drm/i915/i915_params.c @@ -65,6 +65,7 @@ struct i915_params i915 __read_mostly = { .inject_load_failure = 0, .enable_dpcd_backlight = false, .enable_gvt = false, + .enable_dithering = -1, };
module_param_named(modeset, i915.modeset, int, 0400); @@ -257,3 +258,7 @@ MODULE_PARM_DESC(enable_dpcd_backlight, module_param_named(enable_gvt, i915.enable_gvt, bool, 0400); MODULE_PARM_DESC(enable_gvt, "Enable support for Intel GVT-g graphics virtualization host support(default:false)"); + +module_param_named(enable_dithering, i915.enable_dithering, int, 0644); +MODULE_PARM_DESC(enable_dithering, + "Enable dithering (-1=auto [default], 0=force off on all outputs, 1=force on on all outputs)"); diff --git a/drivers/gpu/drm/i915/i915_params.h b/drivers/gpu/drm/i915/i915_params.h index ac844709c97e..7e365cd4fc91 100644 --- a/drivers/gpu/drm/i915/i915_params.h +++ b/drivers/gpu/drm/i915/i915_params.h @@ -54,6 +54,7 @@ func(int, edp_vswing); \ func(int, reset); \ func(unsigned int, inject_load_failure); \ + func(int, enable_dithering); \ /* leave bools at the end to not create holes */ \ func(bool, alpha_support); \ func(bool, enable_cmd_parser); \ diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c index 0e93ec201fe3..bea471a96820 100644 --- a/drivers/gpu/drm/i915/intel_display.c +++ b/drivers/gpu/drm/i915/intel_display.c @@ -10978,6 +10978,11 @@ intel_modeset_pipe_config(struct drm_crtc *crtc, */ pipe_config->dither = (pipe_config->pipe_bpp == 6*3) && !pipe_config->dither_force_disable; + + /* Override of auto-selected dither mode via module parameter? */ + if (i915.enable_dithering != -1) + pipe_config->dither = i915.enable_dithering > 0 ? true : false; + DRM_DEBUG_KMS("hw max bpp: %i, pipe bpp: %i, dithering: %i\n", base_bpp, pipe_config->pipe_bpp, pipe_config->dither);