linux-kernel - Re: [PATCH v8 2/4] drm/panthor: Extend IRQ helpers for mask modification/restoration

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Message-ID: <20260113132303.0c35bb7a@fedora>
Date: Tue, 13 Jan 2026 13:23:03 +0100
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
Cc: Steven Price <steven.price@....com>, Liviu Dudau <liviu.dudau@....com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie
 <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Chia-I Wu
 <olvaffe@...il.com>, Karunika Choo <karunika.choo@....com>,
 kernel@...labora.com, linux-kernel@...r.kernel.org,
 dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v8 2/4] drm/panthor: Extend IRQ helpers for mask
 modification/restoration

On Mon, 12 Jan 2026 15:37:50 +0100
Nicolas Frattaroli <nicolas.frattaroli@...labora.com> wrote:

> The current IRQ helpers do not guarantee mutual exclusion that covers
> the entire transaction from accessing the mask member and modifying the
> mask register.
> 
> This makes it hard, if not impossible, to implement mask modification
> helpers that may change one of these outside the normal
> suspend/resume/isr code paths.
> 
> Add a spinlock to struct panthor_irq that protects both the mask member
> and register. Acquire it in all code paths that access these, but drop
> it before processing the threaded handler function. Then, add the
> aforementioned new helpers: enable_events, and disable_events. They work
> by ORing and NANDing the mask bits.
> 
> resume is changed to no longer have a mask passed, as pirq->mask is
> supposed to be the user-requested mask now, rather than a mirror of the
> INT_MASK register contents. Users of the resume helper are adjusted
> accordingly, including a rather painful refactor in panthor_mmu.c.
> 
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
> ---
>  drivers/gpu/drm/panthor/panthor_device.h |  72 +++++++--
>  drivers/gpu/drm/panthor/panthor_fw.c     |   3 +-
>  drivers/gpu/drm/panthor/panthor_gpu.c    |   2 +-
>  drivers/gpu/drm/panthor/panthor_mmu.c    | 247 ++++++++++++++++---------------
>  drivers/gpu/drm/panthor/panthor_pwr.c    |   2 +-
>  5 files changed, 187 insertions(+), 139 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_device.h b/drivers/gpu/drm/panthor/panthor_device.h
> index 424f6cd1a814..0a29234ac58c 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.h
> +++ b/drivers/gpu/drm/panthor/panthor_device.h
> @@ -84,11 +84,14 @@ struct panthor_irq {
>  	/** @irq: IRQ number. */
>  	int irq;
>  
> -	/** @mask: Current mask being applied to xxx_INT_MASK. */
> +	/** @mask: Values to write to xxx_INT_MASK if active. */
>  	u32 mask;
>  
>  	/** @state: one of &enum panthor_irq_state reflecting the current state. */
>  	atomic_t state;
> +
> +	/** @mask_lock: protects modifications to _INT_MASK and @mask */
> +	spinlock_t mask_lock;

nit: Can we move this mask_lock right after the mask field?