[PATCH xserver] modesetting: Clear drmmode->fb_id before unflipping

[Lyude]

From: Lyude Paul <cpaul at redhat.com>

[fix copied from 40191d82370e in xf86-video-ati]

Without this, we end up setting rotated CRTCs back to their previous
framebuffer right after we perform a rotation. Reproducer:

- Have two monitors connected at the same resolution
- Rotate one monitor from normal straight to inverted
- Watch as the monitor you didn't rotate either freezes or shows intense
  flickering

Signed-off-by: Lyude <cpaul at redhat.com>
---
 hw/xfree86/drivers/modesetting/present.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/hw/xfree86/drivers/modesetting/present.c b/hw/xfree86/drivers/modesetting/present.c
index d65c8c8..9a596de 100644
--- a/hw/xfree86/drivers/modesetting/present.c
+++ b/hw/xfree86/drivers/modesetting/present.c
@@ -626,6 +626,15 @@ ms_present_unflip(ScreenPtr screen, uint64_t event_id)
 	if (!crtc->enabled)
 	    continue;
 
+	/* info->drmmode.fb_id still points to the FB for the last flipped BO.
+	 * Clear it, drmmode_set_mode_major will re-create it
+	 */
+	if (drmmode_crtc->drmmode->fb_id) {
+		drmModeRmFB(drmmode_crtc->drmmode->fd,
+			    drmmode_crtc->drmmode->fb_id);
+		drmmode_crtc->drmmode->fb_id = 0;
+	}
+
 	if (drmmode_crtc->dpms_mode == DPMSModeOn)
 	    crtc->funcs->set_mode_major(crtc, &crtc->mode, crtc->rotation,
 					crtc->x, crtc->y);
-- 
2.5.5