intel_lpe_audio_irq_handler() forwards the LPE audio child IRQ from the
i915 parent IRQ path with generic_handle_irq(). The forwarded child top
half is not an independent hardirq entry point; it inherits the context
of the outer i915 interrupt dispatch path.

This becomes a problem when the parent IRQ runs in threaded context, for
example on PREEMPT_RT or other forced-threading configurations. i915
requests the parent IRQ with IRQF_SHARED and without IRQF_NO_THREAD, so
the forwarded child handler can run with local IRQs enabled. That
violates the expected top-half execution semantics and can trigger an
"enabled interrupts" WARN.

The issue was identified on Linux v6.18.21 by our static analysis tool
and then manually reviewed on the i915 child-IRQ forwarding sites after
commit 8cadce97bf26 ("drm/i915/gsc: mei interrupt top half should be in
irq disabled context") fixed the same helper contract for the GSC path.

It was then validated with a reproducible QEMU no-device parent/child
IRQ harness that registers a threaded parent IRQ and a child IRQ
handler, then exercises both generic_handle_irq() and
generic_handle_irq_safe() under the same threaded parent context. In the
plain-helper phase, the child handler ran with irqs_disabled=0 and
triggered an "enabled interrupts" WARN. In the safe-helper phase, the
same child handler ran with irqs_disabled=1. This is family-level
runtime evidence for the same IRQ forwarding misuse pattern. No
Baytrail/Cherrytrail hardware was available to run the real i915 LPE
path end-to-end.

Use generic_handle_irq_safe() here so the forwarded LPE audio child IRQ
runs with local IRQs disabled even when the outer i915 dispatch path is
threaded.

Link: https://lore.kernel.org/all/20260310115709.2276203-16-dev@lankhorst.se/
Fixes: eef57324d926 ("drm/i915: setup bridge for HDMI LPE audio driver")
Suggested-by: Maarten Lankhorst <dev@lankhorst.se>
Signed-off-by: Runyu Xiao <runyu.xiao@seu.edu.cn>
---
v2:
- Add Link: tag to Maarten's PREEMPT_RT series
- Add Suggested-by: Maarten Lankhorst
- Drop Cc: stable@vger.kernel.org per Sebastian's feedback
- Keep as a standalone patch per Jani's suggestion

 drivers/gpu/drm/i915/display/intel_lpe_audio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_lpe_audio.c b/drivers/gpu/drm/i915/display/intel_lpe_audio.c
index 42284e9928f2..ac1dfd592a9f 100644
--- a/drivers/gpu/drm/i915/display/intel_lpe_audio.c
+++ b/drivers/gpu/drm/i915/display/intel_lpe_audio.c
@@ -263,7 +263,7 @@ void intel_lpe_audio_irq_handler(struct intel_display *display)
 	if (!HAS_LPE_AUDIO(display))
 		return;
 
-	ret = generic_handle_irq(display->audio.lpe.irq);
+	ret = generic_handle_irq_safe(display->audio.lpe.irq);
 	if (ret)
 		drm_err_ratelimited(display->drm,
 				    "error handling LPE audio irq: %d\n", ret);
-- 
2.34.1

On 2026-05-31 23:31:08 [+0800], Runyu Xiao wrote:
> intel_lpe_audio_irq_handler() forwards the LPE audio child IRQ from the
> i915 parent IRQ path with generic_handle_irq(). The forwarded child top
> half is not an independent hardirq entry point; it inherits the context
> of the outer i915 interrupt dispatch path.
…
> 
> Link: https://lore.kernel.org/all/20260310115709.2276203-16-dev@lankhorst.se/
> Fixes: eef57324d926 ("drm/i915: setup bridge for HDMI LPE audio driver")
> Suggested-by: Maarten Lankhorst <dev@lankhorst.se>
> Signed-off-by: Runyu Xiao <runyu.xiao@seu.edu.cn>

If you want to send this as an individual patch, please take Maarten
original patch, add your signed-off by below and send it while keeping
him as Author.

Sebastian