linux-kernel - Re: [PATCH] drm/i915/gsc: mei interrupt top half should be in irq disabled context

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Message-ID: <20250424071553.yT9-dWWM@linutronix.de>
Date: Thu, 24 Apr 2025 09:15:53 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Junxiao Chang <junxiao.chang@...el.com>
Cc: Jani Nikula <jani.nikula@...ux.intel.com>,
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
	Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Tvrtko Ursulin <tursulin@...ulin.net>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Clark Williams <clrkwllms@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev
Subject: Re: [PATCH] drm/i915/gsc: mei interrupt top half should be in irq
 disabled context

On 2025-04-24 14:56:08 [+0800], Junxiao Chang wrote:
> MEI GSC interrupt comes from i915. It has top half and bottom half.
> Top half is called from i915 interrupt handler. It should be in
> irq disabled context.
> 
> With RT kernel, by default i915 IRQ handler is in threaded IRQ. MEI GSC
> top half might be in threaded IRQ context. In this case, local IRQ
> should be disabled for MEI GSC interrupt top half.
> 
> This change fixes A380/A770 GPU boot hang issue with RT kernel.

This should have a Fixes when generic_handle_irq() was introduced. 

> Signed-off-by: Junxiao Chang <junxiao.chang@...el.com>
> ---
>  drivers/gpu/drm/i915/gt/intel_gsc.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_gsc.c b/drivers/gpu/drm/i915/gt/intel_gsc.c
> index 1e925c75fb080..9c72117263f78 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gsc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_gsc.c
> @@ -270,6 +270,9 @@ static void gsc_init_one(struct drm_i915_private *i915, struct intel_gsc *gsc,
>  static void gsc_irq_handler(struct intel_gt *gt, unsigned int intf_id)
>  {
>  	int ret;
> +#ifdef CONFIG_PREEMPT_RT
> +	int irq_disabled_flag;
> +#endif
>  
>  	if (intf_id >= INTEL_GSC_NUM_INTERFACES) {
>  		gt_warn_once(gt, "GSC irq: intf_id %d is out of range", intf_id);
> @@ -284,7 +287,18 @@ static void gsc_irq_handler(struct intel_gt *gt, unsigned int intf_id)
>  	if (gt->gsc.intf[intf_id].irq < 0)
>  		return;
>  
> +#ifdef CONFIG_PREEMPT_RT
> +	/* mei interrupt top half should run in irq disabled context */
> +	irq_disabled_flag = irqs_disabled();
> +	if (!irq_disabled_flag)
> +		local_irq_disable();
> +#endif
>  	ret = generic_handle_irq(gt->gsc.intf[intf_id].irq);

What about generic_handle_irq_safe() instead the whole ifdef show?

> +#ifdef CONFIG_PREEMPT_RT
> +	if (!irq_disabled_flag)
> +		local_irq_enable();
> +#endif
> +
>  	if (ret)
>  		gt_err_ratelimited(gt, "error handling GSC irq: %d\n", ret);
>  }

Sebastian