linux-kernel - [RFC v8 2/9] drm/vblank: Use spin_(un)lock_irq() in drm_crtc_vblank

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Message-Id: <20200627194657.156514-3-lyude@redhat.com>
Date:   Sat, 27 Jun 2020 15:46:50 -0400
From:   Lyude Paul <lyude@...hat.com>
To:     dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org
Cc:     Daniel Vetter <daniel@...ll.ch>,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        linux-kernel@...r.kernel.org (open list)
Subject: [RFC v8 2/9] drm/vblank: Use spin_(un)lock_irq() in drm_crtc_vblank_off()

This got me confused for a bit while looking over this code: I had been
planning on adding some blocking function calls into this function, but
seeing the irqsave/irqrestore variants of spin_(un)lock() didn't make it
very clear whether or not that would actually be safe.

So I went ahead and reviewed every single driver in the kernel that uses
this function, and they all fall into three categories:

* Driver probe code
* ->atomic_disable() callbacks
* Legacy modesetting callbacks

All of these will be guaranteed to have IRQs enabled, which means it's
perfectly safe to block here. Just to make things a little less
confusing to others in the future, let's switch over to
spin_lock_irq()/spin_unlock_irq() to make that fact a little more
obvious.

Signed-off-by: Lyude Paul <lyude@...hat.com>
Reviewed-by: Daniel Vetter <daniel@...ll.ch>
Cc: Ville Syrjälä <ville.syrjala@...ux.intel.com>
---
 drivers/gpu/drm/drm_vblank.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index ce5c1e1d29963..e895f5331fdb4 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -1283,13 +1283,12 @@ void drm_crtc_vblank_off(struct drm_crtc *crtc)
 	struct drm_pending_vblank_event *e, *t;
 
 	ktime_t now;
-	unsigned long irqflags;
 	u64 seq;
 
 	if (drm_WARN_ON(dev, pipe >= dev->num_crtcs))
 		return;
 
-	spin_lock_irqsave(&dev->event_lock, irqflags);
+	spin_lock_irq(&dev->event_lock);
 
 	spin_lock(&dev->vbl_lock);
 	drm_dbg_vbl(dev, "crtc %d, vblank enabled %d, inmodeset %d\n",
@@ -1325,7 +1324,7 @@ void drm_crtc_vblank_off(struct drm_crtc *crtc)
 		drm_vblank_put(dev, pipe);
 		send_vblank_event(dev, e, seq, now);
 	}
-	spin_unlock_irqrestore(&dev->event_lock, irqflags);
+	spin_unlock_irq(&dev->event_lock);
 
 	/* Will be reset by the modeset helpers when re-enabling the crtc by
 	 * calling drm_calc_timestamping_constants(). */
-- 
2.26.2