Attachment 121821 Details for Bug 93746 – First proposed patch to fix this on radeon-kms

[patch] First proposed patch to fix this on radeon-kms

0001-drm-radeon-Don-t-hang-in-radeon_flip_work_func-on-di.patch (text/plain), 3.73 KB, created by Mario Kleiner on 2016-02-17 23:05:11 UTC

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Creator: Mario Kleiner

Created: 2016-02-17 23:05:11 UTC

Size: 3.73 KB

patch

obsolete

>From f99d39fe7031c52a435ba8f07674339dee60c9f0 Mon Sep 17 00:00:00 2001
>From: Mario Kleiner <mario.kleiner.de@gmail.com>
>Date: Wed, 17 Feb 2016 21:48:09 +0100
>Subject: [PATCH] drm/radeon: Don't hang in radeon_flip_work_func on disabled
> crtc.
>
>This fixes a regression introduced in Linux 4.4.
>
>Limit the amount of time radeon_flip_work_func can
>delay programming a page flip, by both limiting the
>maximum amount of time per wait cycle and the maximum
>number of wait cycles. Continue the flip if the limit
>is exceeded, even if that may result in a visual or
>timing glitch.
>
>This is to prevent a hang of page flips, as reported
>in fdo bug #93746: Disconnecting a DisplayPort display
>in parallel to a kms pageflip getting queued can cause
>the following hang of page flips and thereby an unusable
>desktop:
>
>1. kms pageflip ioctl() queues pageflip -> queues execution
>   of radeon_flip_work_func.
>
>2. Hotunplug of display causes the driver to DPMS OFF
>   the unplugged display. Display engine shuts down,
>   scanout no longer moves, but stays at its resting
>   position at start line of vblank.
>
>3. radeon_flip_work_func executes while crtc is off, and
>   due to the non-moving scanout position, the new flip
>   delay code introduced into Linux 4.4 by
>   commit 5b5561b3660d ("drm/radeon: Fixup hw vblank counter/ts..")
>   enters an infinite wait loop.
>
>4. After reconnecting the display, the pageflip continues
>   to hang in 3. and the display doesn't update its view
>   of the desktop.
>
>This patch should fix fdo bug #93746
>
>Reported-by: Bernd Steinhauser <linux@bernd-steinhauser.de>
>Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
>Cc: <stable@vger.kernel.org> # 4.4+
>---
> drivers/gpu/drm/radeon/radeon_display.c | 18 +++++++++++++++---
> 1 file changed, 15 insertions(+), 3 deletions(-)
>
>diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
>index b3bb923..c37eda2 100644
>--- a/drivers/gpu/drm/radeon/radeon_display.c
>+++ b/drivers/gpu/drm/radeon/radeon_display.c
>@@ -403,7 +403,8 @@ static void radeon_flip_work_func(struct work_struct *__work)
> 	struct drm_crtc *crtc = &radeon_crtc->base;
> 	unsigned long flags;
> 	int r;
>-	int vpos, hpos, stat, min_udelay;
>+	int vpos, hpos, stat, min_udelay = 0;
>+	unsigned repcnt = 4;
> 	struct drm_vblank_crtc *vblank = &crtc->dev->vblank[work->crtc_id];
> 
>         down_read(&rdev->exclusive_lock);
>@@ -454,7 +455,7 @@ static void radeon_flip_work_func(struct work_struct *__work)
> 	 * In practice this won't execute very often unless on very fast
> 	 * machines because the time window for this to happen is very small.
> 	 */
>-	for (;;) {
>+	while (repcnt--) {
> 		/* GET_DISTANCE_TO_VBLANKSTART returns distance to real vblank
> 		 * start in hpos, and to the "fudged earlier" vblank start in
> 		 * vpos.
>@@ -472,13 +473,24 @@ static void radeon_flip_work_func(struct work_struct *__work)
> 		/* Sleep at least until estimated real start of hw vblank */
> 		spin_unlock_irqrestore(&crtc->dev->event_lock, flags);
> 		min_udelay = (-hpos + 1) * max(vblank->linedur_ns / 1000, 5);
>+		if (min_udelay > vblank->framedur_ns / 2000) {
>+			/* Don't wait ridiculously long - something is wrong */
>+			repcnt = 0;
>+			break;
>+		}
> 		usleep_range(min_udelay, 2 * min_udelay);
> 		spin_lock_irqsave(&crtc->dev->event_lock, flags);
> 	};
> 
>+	if (!repcnt)
>+		DRM_DEBUG_DRIVER("Delay problem on crtc %d: min_udelay %d, "
>+				 "framedur %d, linedur %d, stat %d, vpos %d, "
>+				 "hpos %d\n", work->crtc_id, min_udelay,
>+				 vblank->framedur_ns / 1000,
>+				 vblank->linedur_ns / 1000, stat, vpos, hpos);
>+
> 	/* do the flip (mmio) */
> 	radeon_page_flip(rdev, radeon_crtc->crtc_id, work->base);
>-
> 	radeon_crtc->flip_status = RADEON_FLIP_SUBMITTED;
> 	spin_unlock_irqrestore(&crtc->dev->event_lock, flags);
> 	up_read(&rdev->exclusive_lock);
>-- 
>1.9.1
>

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