[PATCH] drm/tilcdc: Force recalculation of vrefresh in tilcdc_crtc_set_mode()

[Jyri Sarha]

We are using the vrefresh to check if we are too close to vertical
sync to update the two framebuffer DMA registers and risk a
collision. The vrefresh is coming from user space and normally it is
not used for anything. For instance xserver leaves vrefresh to zero
causing a division by zero when setting the mode. We want to make sure
the value is valid and force its recalculation in
tilcdc_crtc_set_mode().

Reported-by: Kevin Hao <kexin.hao at windriver.com>
Fixes: 11abbc9f39e0 ("drm/tilcdc: Set framebuffer DMA address to HW only if CRTC is enabled")
Cc: <stable at vger.kernel.org> # v4.11+
Signed-off-by: Jyri Sarha <jsarha at ti.com>
---
 drivers/gpu/drm/tilcdc/tilcdc_crtc.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
index 704db24..aa5e87c 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
+++ b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
@@ -459,6 +459,16 @@ static void tilcdc_crtc_set_mode(struct drm_crtc *crtc)
 	drm_framebuffer_get(fb);
 
 	crtc->hwmode = crtc->state->adjusted_mode;
+
+	/* We are using the vrefresh to check if we are too close to
+	 * vertical sync to update the two framebuffer DMA registers
+	 * and risk a collision. The vrefresh is coming from user
+	 * space and normally it is not used for anything. We want to
+	 * make sure the value is valid and force its recalculation
+	 * here.
+	 */
+	crtc->hwmode.vrefresh = 0;
+	crtc->hwmode.vrefresh = drm_mode_vrefresh(&crtc->hwmode);
 }
 
 static void tilcdc_crtc_enable(struct drm_crtc *crtc)
-- 
1.9.1


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