Re: [PATCH 1/3] drm: Add infrastructure to allow seamless mode switches

On Thu, Apr 21, 2022 at 12:22:03PM -0700, José Roberto de Souza wrote:

Intel hardware supports change between modes with different refresh rates without any glitches or visual artifacts, that feature is called seamless DRRS.

So far i915 driver was automatically changing between preferred panel mode and lower refresh rate mode based on idleness but ChromeOS compositor team is requesting to be in control of the mode switch. So for a certain types of content it can switch to mode with a lower refresh rate without user noticing a thing and saving power.

This seamless mode switch will be triggered when user-space dispatch a atomic commit with the new mode and clears the DRM_MODE_ATOMIC_ALLOW_MODESET flag.

A driver that don't implement atomic_seamless_mode_switch_check function will continue to fail in the atomic check phase with "[CRTC:%d:%s] requires full modeset" debug message. While a driver that implements it and support the seamless change between old and new mode will return 0 otherwise it should return the appropried errno.

So here adding basic drm infrastructure to that be supported by i915 and other drivers.

I don't see the need for any extra infrastructure for this.

I think we just need: - fix the fastset code to not suck - reprogram M/N during fastset - calculate eDP link params using panel's highest refresh rate mode to make sure we get the same link params for all refresh rates

Cc: Vidya Srinivas vidya.srinivas@intel.com Cc: Sean Paul seanpaul@chromium.org Cc: Ville Syrjälä ville.syrjala@linux.intel.com Signed-off-by: José Roberto de Souza jose.souza@intel.com

---

drivers/gpu/drm/drm_atomic.c | 1 + drivers/gpu/drm/drm_atomic_helper.c | 16 +++++++++++++++ drivers/gpu/drm/drm_atomic_state_helper.c | 1 + include/drm/drm_crtc.h | 25 +++++++++++++++++++++++ 4 files changed, 43 insertions(+)

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c index 58c0283fb6b0c..21525f9f4b4c1 100644 --- a/drivers/gpu/drm/drm_atomic.c +++ b/drivers/gpu/drm/drm_atomic.c @@ -437,6 +437,7 @@ static void drm_atomic_crtc_print_state(struct drm_printer *p, drm_printf(p, "\tself_refresh_active=%d\n", state->self_refresh_active); drm_printf(p, "\tplanes_changed=%d\n", state->planes_changed); drm_printf(p, "\tmode_changed=%d\n", state->mode_changed);

• drm_printf(p, "\tseamless_mode_changed=%d\n", state->seamless_mode_changed); drm_printf(p, "\tactive_changed=%d\n", state->active_changed); drm_printf(p, "\tconnectors_changed=%d\n", state->connectors_changed); drm_printf(p, "\tcolor_mgmt_changed=%d\n", state->color_mgmt_changed);

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c index 9603193d2fa13..e6f3a966f7b86 100644 --- a/drivers/gpu/drm/drm_atomic_helper.c +++ b/drivers/gpu/drm/drm_atomic_helper.c @@ -631,6 +631,22 @@ drm_atomic_helper_check_modeset(struct drm_device *dev, drm_dbg_atomic(dev, "[CRTC:%d:%s] mode changed\n", crtc->base.id, crtc->name); new_crtc_state->mode_changed = true;

• 	if (!state->allow_modeset &&
  

• 	    crtc->funcs->atomic_seamless_mode_switch_check) {
  

• 		ret = crtc->funcs->atomic_seamless_mode_switch_check(state, crtc);
  

• 		if (ret == -EOPNOTSUPP) {
  

• 			drm_dbg_atomic(dev, "[CRTC:%d:%s] Seamless mode switch not supported\n",
  

• 				       crtc->base.id, crtc->name);
  

• 			return ret;
  

• 		}
  

• 		if (ret < 0)
  

• 			return ret;
  

• 		new_crtc_state->seamless_mode_changed = true;
  

• 		new_crtc_state->mode_changed = false;
  

• 	}
  

  }

  if (old_crtc_state->enable != new_crtc_state->enable) {

diff --git a/drivers/gpu/drm/drm_atomic_state_helper.c b/drivers/gpu/drm/drm_atomic_state_helper.c index 3b6d3bdbd0996..c093073ea6e11 100644 --- a/drivers/gpu/drm/drm_atomic_state_helper.c +++ b/drivers/gpu/drm/drm_atomic_state_helper.c @@ -142,6 +142,7 @@ void __drm_atomic_helper_crtc_duplicate_state(struct drm_crtc *crtc, if (state->gamma_lut) drm_property_blob_get(state->gamma_lut); state->mode_changed = false;

• state->seamless_mode_changed = false; state->active_changed = false; state->planes_changed = false; state->connectors_changed = false;

diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h index a70baea0636ca..b7ce378d679d3 100644 --- a/include/drm/drm_crtc.h +++ b/include/drm/drm_crtc.h @@ -140,6 +140,16 @@ struct drm_crtc_state { */ bool mode_changed : 1;

• /**

• * @seamless_mode_changed: @mode has been changed but user-space
  

• * is requesting to change to the new mode with a fastset and driver
  

• * supports this request.
  

• * To be used by drivers to steer the atomic commit control flow to
  

• * appropriate paths to change mode without any visual corruption.
  

• * Never set together with @mode_changed.
  

• */
  

• bool seamless_mode_changed : 1;
• /**
  • @active_changed: @active has been toggled. Used by the atomic
  • helpers and drivers to steer the atomic commit control flow. See also

@@ -939,6 +949,21 @@ struct drm_crtc_funcs { int *max_error, ktime_t *vblank_time, bool in_vblank_irq);

• /**

• * @atomic_seamless_mode_switch_check
  

• *
  

• * Called when user-space wants to change mode without do a modeset.
  

• * Drivers can optionally support do a mode switch without any visual
  

• * corruption when changing between certain modes.
  

• *
  

• * Returns:
  

• * Zero if possible to seamless switch mode, -EOPNOTSUPP if not
  

• * supported seamless mode change or appropriate errno if an error
  

• * happened.
  

• */
  

• int (*atomic_seamless_mode_switch_check)(struct drm_atomic_state *state,

• 				 struct drm_crtc *crtc);
  

};

/**

2.36.0