[PATCH v2] drm/msm/dpu: compute the CRTC bandwidth from the state being checked

[PATCH v2] drm/msm/dpu: compute the CRTC bandwidth from the state being checked

[Joonhoe Kim]

_dpu_core_perf_calc_bw() is called with the new CRTC state but sums
plane_fetch_bw over drm_atomic_crtc_for_each_plane(), i.e. the planes
of the committed state. When the CRTC is re-enabled (DPMS on, system
resume) the committed state has no planes attached, so the check
computes bw_ctl = 0 and the display runs without an average bandwidth
vote on the MDP path until some later commit changes a plane -- which
may not happen for a long time on a static screen such as a lock
screen.

Seen on a Lenovo TB323FU (SM8850) through the interconnect and DPU
tracepoints: after DPMS off/on or s2idle, dpu_perf_crtc_update reported
bw_ctl=0 and qnm_mdp was left at avg_bw=0 (peak 800000) instead of the
3728793 kBps voted before, until the next mode change.

Iterate the plane states of the CRTC state being checked instead.
drm_atomic_crtc_state_for_each_plane_state() falls back to the current
plane state for planes that are not part of the commit, so the result
is unchanged for commits that do touch the planes.

With this, bw_ctl is 3728793600 right after DPMS on and after resume.
Only tested on this device.

Fixes: c33b7c0389e1 ("drm/msm/dpu: add support for clk and bw scaling for display")
Assisted-by: LLM
Signed-off-by: Joonhoe Kim <26rote@gmail.com>
---
Changes in v2:
- Drop the code comment that repeated the commit message. [Dmitry]
- Link to v1: https://lore.kernel.org/all/20260929130633.977-1-26rote@gmail.com/

_dpu_core_perf_calc_clk() walks the planes the same way; it is not
touched here since I have not seen a wrong clock vote from it.

 drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.c | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.c
index fea173e37464..9fa55904dba1 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.c
@@ -54,24 +54,19 @@ u64 dpu_core_perf_adjusted_mode_clk(u64 mode_clk_rate,
 /**
  * _dpu_core_perf_calc_bw() - to calculate BW per crtc
  * @perf_cfg: performance configuration
- * @crtc: pointer to a crtc
+ * @state: the CRTC state
  * Return: returns aggregated BW for all planes in crtc.
  */
 static u64 _dpu_core_perf_calc_bw(const struct dpu_perf_cfg *perf_cfg,
-		struct drm_crtc *crtc)
+		struct drm_crtc_state *state)
 {
 	struct drm_plane *plane;
-	struct dpu_plane_state *pstate;
+	const struct drm_plane_state *plane_state;
 	u64 crtc_plane_bw = 0;
 	u32 bw_factor;
 
-	drm_atomic_crtc_for_each_plane(plane, crtc) {
-		pstate = to_dpu_plane_state(plane->state);
-		if (!pstate)
-			continue;
-
-		crtc_plane_bw += pstate->plane_fetch_bw;
-	}
+	drm_atomic_crtc_state_for_each_plane_state(plane, plane_state, state)
+		crtc_plane_bw += to_dpu_plane_state(plane_state)->plane_fetch_bw;
 
 	bw_factor = perf_cfg->bw_inefficiency_factor;
 	if (bw_factor) {
@@ -131,7 +126,7 @@ static void _dpu_core_perf_calc_crtc(const struct dpu_core_perf *core_perf,
 		return;
 	}
 
-	perf->bw_ctl = _dpu_core_perf_calc_bw(perf_cfg, crtc);
+	perf->bw_ctl = _dpu_core_perf_calc_bw(perf_cfg, state);
 	perf->max_per_pipe_ib = perf_cfg->min_dram_ib;
 	perf->core_clk_rate = _dpu_core_perf_calc_clk(perf_cfg, crtc, state);
 	DRM_DEBUG_ATOMIC(

base-commit: 6375e61c01e93e35ee7acd336a689ac1fae4b509
-- 
2.43.0

Re: [PATCH v2] drm/msm/dpu: compute the CRTC bandwidth from the state being checked

[Dmitry Baryshkov]

On Fri, Oct 02, 2026 at 10:06:56PM +0900, Joonhoe Kim wrote:
> _dpu_core_perf_calc_bw() is called with the new CRTC state but sums
> plane_fetch_bw over drm_atomic_crtc_for_each_plane(), i.e. the planes
> of the committed state. When the CRTC is re-enabled (DPMS on, system
> resume) the committed state has no planes attached, so the check
> computes bw_ctl = 0 and the display runs without an average bandwidth
> vote on the MDP path until some later commit changes a plane -- which
> may not happen for a long time on a static screen such as a lock
> screen.
> 
> Seen on a Lenovo TB323FU (SM8850) through the interconnect and DPU
> tracepoints: after DPMS off/on or s2idle, dpu_perf_crtc_update reported
> bw_ctl=0 and qnm_mdp was left at avg_bw=0 (peak 800000) instead of the
> 3728793 kBps voted before, until the next mode change.
> 
> Iterate the plane states of the CRTC state being checked instead.
> drm_atomic_crtc_state_for_each_plane_state() falls back to the current
> plane state for planes that are not part of the commit, so the result
> is unchanged for commits that do touch the planes.
> 
> With this, bw_ctl is 3728793600 right after DPMS on and after resume.
> Only tested on this device.
> 
> Fixes: c33b7c0389e1 ("drm/msm/dpu: add support for clk and bw scaling for display")
> Assisted-by: LLM
> Signed-off-by: Joonhoe Kim <26rote@gmail.com>
> ---
> Changes in v2:
> - Drop the code comment that repeated the commit message. [Dmitry]
> - Link to v1: https://lore.kernel.org/all/20260929130633.977-1-26rote@gmail.com/
> 
> _dpu_core_perf_calc_clk() walks the planes the same way; it is not
> touched here since I have not seen a wrong clock vote from it.
> 
>  drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.c | 17 ++++++-----------
>  1 file changed, 6 insertions(+), 11 deletions(-)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>


-- 
With best wishes
Dmitry