On 7/10/26 22:31, Alex Hung wrote:
[WHY]
The out fence was signalled on the first vblank after arming, before the
DMA finished copying, and the old code worked around this with an
mdelay() in the IRQ handler.
[HOW]
Hold a vblank reference while writeback is pending and signal the out
fence on the second vblank instead of using mdelay(). Add
amdgpu_dm_crtc_complete_writeback() to finish and clean up writeback
from both the IRQ and teardown paths.
This can be verified by running IGT's kms_writeback 20 times without
timeout errors.
Assisted-by: Copilot:Claude-Opus-4.8
Signed-off-by: Alex Hung <[email protected]>
Reviewed-by: Mario Limonciello (AMD) <[email protected]>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_mode.h | 1 +
.../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 ++
.../drm/amd/display/amdgpu_dm/amdgpu_dm_irq.c | 33 ++++++++++---------
3 files changed, 21 insertions(+), 15 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_mode.h
b/drivers/gpu/drm/amd/amdgpu/amdgpu_mode.h
index 8069fc41cc7f..7c784277396a 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_mode.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_mode.h
@@ -509,6 +509,7 @@ struct amdgpu_crtc {
struct drm_pending_vblank_event *event;
bool wb_pending;
+ bool wb_frame_done;
bool wb_enabled;
struct drm_writeback_connector *wb_conn;
};
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index d67dcaa3fa8f..0f5453649200 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -4521,6 +4521,7 @@ bool amdgpu_dm_crtc_complete_writeback(struct amdgpu_crtc
*acrtc)
spin_lock_irqsave(&acrtc->wb_conn->job_lock, flags);
pending = acrtc->wb_pending;
acrtc->wb_pending = false;
+ acrtc->wb_frame_done = false;
spin_unlock_irqrestore(&acrtc->wb_conn->job_lock, flags);
if (!pending)
@@ -4988,6 +4989,7 @@ static void dm_set_writeback(struct
amdgpu_display_manager *dm,
* cannot run its matching vblank_put before this get.
*/
WARN_ON(drm_crtc_vblank_get(&acrtc->base));
+ acrtc->wb_frame_done = false;
acrtc->wb_pending = true;
}
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_irq.c
b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_irq.c
index c5467f34c51f..4de7fb264cb2 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_irq.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_irq.c
@@ -1974,23 +1974,26 @@ static void dm_crtc_high_irq(void *interrupt_params)
return;
if (acrtc->wb_conn && acrtc->wb_pending) {
- struct dc_stream_state *stream = acrtc->dm_irq_params.stream;
- unsigned int v_total, refresh_hz;
-
- v_total = stream->adjust.v_total_max ?
- stream->adjust.v_total_max : stream->timing.v_total;
- refresh_hz = div_u64((uint64_t) stream->timing.pix_clk_100hz *
- 100LL, (v_total * stream->timing.h_total));
- mdelay(1000 / refresh_hz);
-
- /*
- * Completion (signalling the out fence and releasing the vblank
- * reference taken in dm_set_writeback()) is handled by the
shared
- * helper, which is also used by the teardown path.
- */
- if (amdgpu_dm_crtc_complete_writeback(acrtc))
+ if (acrtc->wb_frame_done) {
+ /*
+ * Second vblank: the DMA for the captured frame has
+ * had a full frame period to flush to memory. Signal
+ * the out fence now.
+ */
+ amdgpu_dm_crtc_complete_writeback(acrtc);
+ } else {
+ /*
+ * First vblank after arming: the frame has been
+ * scanned out and the DMA is finishing. Disable
+ * writeback immediately to prevent the hardware from
+ * starting a new capture that would overwrite the
+ * buffer. Signal completion on the next vblank to
+ * ensure the DMA is fully flushed to memory.
+ */
dc_stream_fc_disable_writeback(adev->dm.dc,
acrtc->dm_irq_params.stream, 0);
+ acrtc->wb_frame_done = true;
+ }
}
vrr_active = amdgpu_dm_crtc_vrr_active_irq(acrtc);
--
2.43.0
