starfive-tech/linux.git/drivers/gpu, branch rt-linux-release

drm/i915: Drop the irqs_disabled() check

2023-11-06T11:24:48+00:00

The !irqs_disabled() check triggers on PREEMPT_RT even with i915_sched_engine::lock acquired. The reason is the lock is transformed into a sleeping lock on PREEMPT_RT and does not disable interrupts. There is no need to check for disabled interrupts. The lockdep annotation below already check if the lock has been acquired by the caller and will yell if the interrupts are not disabled. Remove the !irqs_disabled() check. Reported-by: Maarten Lankhorst Signed-off-by: Sebastian Andrzej Siewior

drm/i915/gt: Use spin_lock_irq() instead of local_irq_disable() + spin_lock()

2023-11-06T11:24:48+00:00

execlists_dequeue() is invoked from a function which uses local_irq_disable() to disable interrupts so the spin_lock() behaves like spin_lock_irq(). This breaks PREEMPT_RT because local_irq_disable() + spin_lock() is not the same as spin_lock_irq(). execlists_dequeue_irq() and execlists_dequeue() has each one caller only. If intel_engine_cs::active::lock is acquired and released with the _irq suffix then it behaves almost as if execlists_dequeue() would be invoked with disabled interrupts. The difference is the last part of the function which is then invoked with enabled interrupts. I can't tell if this makes a difference. From looking at it, it might work to move the last unlock at the end of the function as I didn't find anything that would acquire the lock again. Reported-by: Clark Williams Signed-off-by: Sebastian Andrzej Siewior Reviewed-by: Maarten Lankhorst

drm/i915/gt: Queue and wait for the irq_work item.

2023-11-06T11:24:48+00:00

Disabling interrupts and invoking the irq_work function directly breaks on PREEMPT_RT. PREEMPT_RT does not invoke all irq_work from hardirq context because some of the user have spinlock_t locking in the callback function. These locks are then turned into a sleeping locks which can not be acquired with disabled interrupts. Using irq_work_queue() has the benefit that the irqwork will be invoked in the regular context. In general there is "no" delay between enqueuing the callback and its invocation because the interrupt is raised right away on architectures which support it (which includes x86). Use irq_work_queue() + irq_work_sync() instead invoking the callback directly. Reported-by: Clark Williams Signed-off-by: Sebastian Andrzej Siewior Reviewed-by: Maarten Lankhorst

drm/i915: skip DRM_I915_LOW_LEVEL_TRACEPOINTS with NOTRACE

2023-11-06T11:24:48+00:00

The order of the header files is important. If this header file is included after tracepoint.h was included then the NOTRACE here becomes a nop. Currently this happens for two .c files which use the tracepoitns behind DRM_I915_LOW_LEVEL_TRACEPOINTS. Cc: Steven Rostedt Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Thomas Gleixner

drm/i915: Disable tracing points on PREEMPT_RT

2023-11-06T11:24:48+00:00

Luca Abeni reported this: | BUG: scheduling while atomic: kworker/u8:2/15203/0x00000003 | CPU: 1 PID: 15203 Comm: kworker/u8:2 Not tainted 4.19.1-rt3 #10 | Call Trace: | rt_spin_lock+0x3f/0x50 | gen6_read32+0x45/0x1d0 [i915] | g4x_get_vblank_counter+0x36/0x40 [i915] | trace_event_raw_event_i915_pipe_update_start+0x7d/0xf0 [i915] The tracing events use trace_i915_pipe_update_start() among other events use functions acquire spinlock_t locks which are transformed into sleeping locks on PREEMPT_RT. A few trace points use intel_get_crtc_scanline(), others use ->get_vblank_counter() wich also might acquire a sleeping locks on PREEMPT_RT. At the time the arguments are evaluated within trace point, preemption is disabled and so the locks must not be acquired on PREEMPT_RT. Based on this I don't see any other way than disable trace points on PREMPT_RT. Reported-by: Luca Abeni Cc: Steven Rostedt Signed-off-by: Sebastian Andrzej Siewior

drm/i915: Don't check for atomic context on PREEMPT_RT

2023-11-06T11:24:48+00:00

The !in_atomic() check in _wait_for_atomic() triggers on PREEMPT_RT because the uncore::lock is a spinlock_t and does not disable preemption or interrupts. Changing the uncore:lock to a raw_spinlock_t doubles the worst case latency on an otherwise idle testbox during testing. Therefore I'm currently unsure about changing this. Link: https://lore.kernel.org/all/20211006164628.s2mtsdd2jdbfyf7g@linutronix.de/ Signed-off-by: Sebastian Andrzej Siewior

drm/i915: Don't disable interrupts on PREEMPT_RT during atomic updates

2023-11-06T11:24:48+00:00

Commit 8d7849db3eab7 ("drm/i915: Make sprite updates atomic") started disabling interrupts across atomic updates. This breaks on PREEMPT_RT because within this section the code attempt to acquire spinlock_t locks which are sleeping locks on PREEMPT_RT. According to the comment the interrupts are disabled to avoid random delays and not required for protection or synchronisation. If this needs to happen with disabled interrupts on PREEMPT_RT, and the whole section is restricted to register access then all sleeping locks need to be acquired before interrupts are disabled and some function maybe moved after enabling interrupts again. This includes: - prepare_to_wait() + finish_wait() due its wake queue. - drm_crtc_vblank_put() -> vblank_disable_fn() drm_device::vbl_lock. - skl_pfit_enable(), intel_update_plane(), vlv_atomic_update_fifo() and maybe others due to intel_uncore::lock - drm_crtc_arm_vblank_event() due to drm_device::event_lock and drm_device::vblank_time_lock. Don't disable interrupts on PREEMPT_RT during atomic updates. [bigeasy: drop local locks, commit message] Signed-off-by: Mike Galbraith Signed-off-by: Sebastian Andrzej Siewior

drm/i915: Use preempt_disable/enable_rt() where recommended

2023-11-06T11:24:48+00:00

Mario Kleiner suggest in commit ad3543ede630f ("drm/intel: Push get_scanout_position() timestamping into kms driver.") a spots where preemption should be disabled on PREEMPT_RT. The difference is that on PREEMPT_RT the intel_uncore::lock disables neither preemption nor interrupts and so region remains preemptible. The area covers only register reads and writes. The part that worries me is: - __intel_get_crtc_scanline() the worst case is 100us if no match is found. - intel_crtc_scanlines_since_frame_timestamp() not sure how long this may take in the worst case. It was in the RT queue for a while and nobody complained. Disable preemption on PREEPMPT_RT during timestamping. [bigeasy: patch description.] Cc: Mario Kleiner Signed-off-by: Mike Galbraith Signed-off-by: Thomas Gleixner Signed-off-by: Sebastian Andrzej Siewior

drm/i915: Don't disable interrupts and pretend a lock as been acquired in __timeline_mark_lock().

2023-11-06T11:24:47+00:00

This is a revert of commits d67739268cf0e ("drm/i915/gt: Mark up the nested engine-pm timeline lock as irqsafe") 6c69a45445af9 ("drm/i915/gt: Mark context->active_count as protected by timeline->mutex") The existing code leads to a different behaviour depending on whether lockdep is enabled or not. Any following lock that is acquired without disabling interrupts (but needs to) will not be noticed by lockdep. This it not just a lockdep annotation but is used but an actual mutex_t that is properly used as a lock but in case of __timeline_mark_lock() lockdep is only told that it is acquired but no lock has been acquired. It appears that its purpose is just satisfy the lockdep_assert_held() check in intel_context_mark_active(). The other problem with disabling interrupts is that on PREEMPT_RT interrupts are also disabled which leads to problems for instance later during memory allocation. Add a CONTEXT_IS_PARKED bit to intel_engine_cs and set_bit/clear_bit it instead of mutex_acquire/mutex_release. Use test_bit in the two identified spots which relied on the lockdep annotation. Cc: Peter Zijlstra Signed-off-by: Sebastian Andrzej Siewior

Merge tag 'JH7110_515_SDK_v5.8.2' into vf2-515-devel

2023-10-26T11:04:20+00:00