From 106b4a2a78b2a2f14885604891957b84bba502db Mon Sep 17 00:00:00 2001 From: Adrian Betschart Date: Fri, 11 Sep 2026 17:13:14 +0200 Subject: drm/amd/display: Try RGB before YCbCr 4:4:4 in stream validation amdgpu_dm_create_validate_stream_for_sink() walks encoding_order[] and uses the first encoding that validates. YCbCr 4:4:4 is listed before RGB, so an HDMI sink that advertises 4:4:4 gets YCbCr 4:4:4 whenever the "color format" property is left at AUTO, even though RGB fits the same link. That contradicts the documented AUTO behaviour for HDMI in enum drm_connector_color_format (RGB, falling back to YCbCr 4:2:0 only when the bandwidth is not available or the mode is 4:2:0-only), which the amdgpu implementation of the property also describes. It also leaves the "Broadcast RGB" property without effect on such sinks, since the quantization range it selects only applies to RGB output. Try RGB first. The mask still holds every encoding the sink supports, so a mode that cannot carry RGB falls back exactly as before. For reference, v7.2 picked RGB here unless YCbCr 4:4:4 was forced through debugfs, while earlier kernels picked YCbCr 4:4:4 for any HDMI sink that advertised it. Fixes: 0b0ff65d3ca1 ("drm/amd/display: Refactor stream validation") Suggested-by: Adolfo Rodrigues Assisted-by: Claude Code:claude-fable-5-1 Signed-off-by: Adrian Betschart Reviewed-by: Fangzhi Zuo Tested-by: Adolfo Rodrigues Tested-by: Daniel Wheeler Signed-off-by: Alex Deucher (cherry picked from commit 7de432bc753133764dc40d37f9388da56de251e7) --- samples/workqueue/stall_detector/Makefile | 1 + samples/workqueue/stall_detector/wq_stall.c | 98 +++++++++++++++++++++++++++++ 2 files changed, 99 insertions(+) create mode 100644 samples/workqueue/stall_detector/Makefile create mode 100644 samples/workqueue/stall_detector/wq_stall.c (limited to 'samples/workqueue') diff --git a/samples/workqueue/stall_detector/Makefile b/samples/workqueue/stall_detector/Makefile new file mode 100644 index 000000000..8849e85e9 --- /dev/null +++ b/samples/workqueue/stall_detector/Makefile @@ -0,0 +1 @@ +obj-m += wq_stall.o diff --git a/samples/workqueue/stall_detector/wq_stall.c b/samples/workqueue/stall_detector/wq_stall.c new file mode 100644 index 000000000..6f4a497b1 --- /dev/null +++ b/samples/workqueue/stall_detector/wq_stall.c @@ -0,0 +1,98 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * wq_stall - Test module for the workqueue stall detector. + * + * Deliberately creates a workqueue stall so the watchdog fires and + * prints diagnostic output. Useful for verifying that the stall + * detector correctly identifies stuck workers and produces useful + * backtraces. + * + * The stall is triggered by clearing PF_WQ_WORKER before sleeping, + * which hides the worker from the concurrency manager. A second + * work item queued on the same pool then sits in the worklist with + * no worker available to process it. + * + * After ~30s the workqueue watchdog fires: + * BUG: workqueue lockup - pool cpus=N ... + * + * Build: + * make -C M=samples/workqueue/stall_detector modules + * + * Copyright (c) 2026 Meta Platforms, Inc. and affiliates. + * Copyright (c) 2026 Breno Leitao + */ + +#include +#include +#include +#include +#include + +static DECLARE_WAIT_QUEUE_HEAD(stall_wq_head); +static atomic_t wake_condition = ATOMIC_INIT(0); +static struct work_struct stall_work1; +static struct work_struct stall_work2; + +static void stall_work2_fn(struct work_struct *work) +{ + pr_info("wq_stall: second work item finally ran\n"); +} + +static void stall_work1_fn(struct work_struct *work) +{ + pr_info("wq_stall: first work item running on cpu %d\n", + raw_smp_processor_id()); + + /* + * Queue second item while we're still counted as running + * (pool->nr_running > 0). Since schedule_work() on a per-CPU + * workqueue targets raw_smp_processor_id(), item 2 lands on the + * same pool. __queue_work -> kick_pool -> need_more_worker() + * sees nr_running > 0 and does NOT wake a new worker. + */ + schedule_work(&stall_work2); + + /* + * Hide from the workqueue concurrency manager. Without + * PF_WQ_WORKER, schedule() won't call wq_worker_sleeping(), + * so nr_running is never decremented and no replacement + * worker is created. Item 2 stays stuck in pool->worklist. + */ + current->flags &= ~PF_WQ_WORKER; + + pr_info("wq_stall: entering wait_event_idle (PF_WQ_WORKER cleared)\n"); + pr_info("wq_stall: expect 'BUG: workqueue lockup' in ~30-60s\n"); + wait_event_idle(stall_wq_head, atomic_read(&wake_condition) != 0); + + /* Restore so process_one_work() cleanup works correctly */ + current->flags |= PF_WQ_WORKER; + pr_info("wq_stall: woke up, PF_WQ_WORKER restored\n"); +} + +static int __init wq_stall_init(void) +{ + pr_info("wq_stall: loading\n"); + + INIT_WORK(&stall_work1, stall_work1_fn); + INIT_WORK(&stall_work2, stall_work2_fn); + schedule_work(&stall_work1); + + return 0; +} + +static void __exit wq_stall_exit(void) +{ + pr_info("wq_stall: unloading\n"); + atomic_set(&wake_condition, 1); + wake_up(&stall_wq_head); + flush_work(&stall_work1); + flush_work(&stall_work2); + pr_info("wq_stall: all work flushed, module unloaded\n"); +} + +module_init(wq_stall_init); +module_exit(wq_stall_exit); + +MODULE_LICENSE("GPL"); +MODULE_DESCRIPTION("Reproduce workqueue stall caused by PF_WQ_WORKER misuse"); +MODULE_AUTHOR("Breno Leitao "); -- cgit v1.3.1