Re: [PATCH v9 4/8] drm/i915/dsb: Set DSB_SKIP_WAITS_EN chicken bit for LunarLake and onwards

[Nautiyal, Ankit K]

On 12/23/2025 4:21 PM, Jouni Högander wrote:
On LunarLake we are using TRANS_PUSH mechanism to trigger "Frame Change"
event. This way we have more control on when PSR HW is woken up. I.e. not
every display register write is triggering sending update. This allows us
setting DSB_SKIP_WAITS_EN chicken bit as well.

Signed-off-by: Jouni Högander <jouni.hogan...@intel.com>
---
  drivers/gpu/drm/i915/display/intel_dsb.c | 15 +++++++++++----
  1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dsb.c 
b/drivers/gpu/drm/i915/display/intel_dsb.c
index ec2a3fb171ab..19a99f82f413 100644
--- a/drivers/gpu/drm/i915/display/intel_dsb.c
+++ b/drivers/gpu/drm/i915/display/intel_dsb.c
@@ -17,6 +17,7 @@
  #include "intel_dsb.h"
  #include "intel_dsb_buffer.h"
  #include "intel_dsb_regs.h"
+#include "intel_psr.h"
  #include "intel_vblank.h"
  #include "intel_vrr.h"
  #include "skl_watermark.h"
@@ -166,18 +167,24 @@ static int dsb_scanline_to_hw(struct intel_atomic_state 
*state,
   * definitely do not want to skip vblank wait. We also have concern what comes
   * to skipping vblank evasion. I.e. arming registers are latched before we 
have
   * managed writing them. Due to these reasons we are not setting
- * DSB_SKIP_WAITS_EN.
+ * DSB_SKIP_WAITS_EN except when using TRANS_PUSH mechanism to trigger
+ * "frame change" event.
   */
  static u32 dsb_chicken(struct intel_atomic_state *state,
                       struct intel_crtc *crtc)
  {
+       const struct intel_crtc_state *new_crtc_state =
+               intel_atomic_get_new_crtc_state(state, crtc);
+       u32 chicken = intel_psr_use_trans_push(new_crtc_state) ?
+               DSB_SKIP_WAITS_EN : 0;


I have a query regarding Panel Replay. Let's say Panel Replay is enabled.

crtc_state->has_psr will be set for Panel Replay as well so 
DSB_SKIP_WAITS_EN bit gets set.

As per the bspec: "When set, this will enable the DSB to jump from WAIT 
for Vblank, wait for scanline number, in range and out of range states 
to IDLE state when PSR and PSR2 is entered."

When it says "PSR and PSR2 is entered", does this apply to Panel Replay 
as well? Meaning in case of Panel Replay will the wait be skipped?


Regards,

Ankit

+
        if (pre_commit_is_vrr_active(state, crtc))
-               return DSB_CTRL_WAIT_SAFE_WINDOW |
+               chicken |= DSB_CTRL_WAIT_SAFE_WINDOW |
                        DSB_CTRL_NO_WAIT_VBLANK |
                        DSB_INST_WAIT_SAFE_WINDOW |
                        DSB_INST_NO_WAIT_VBLANK;
-       else
-               return 0;
+
+       return chicken;
  }
  
  static bool assert_dsb_has_room(struct intel_dsb *dsb)