linux-kernel - [PATCH] drm/atmel-hlcdc: prevent divide by zero

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Date:   Tue, 8 Jan 2019 12:31:36 +0000
From:   Peter Rosin <peda@...ntia.se>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Peter Rosin <peda@...ntia.se>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        David Airlie <airlied@...ux.ie>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: [PATCH] drm/atmel-hlcdc: prevent divide by zero

While trying to temporarily hide a plane, one thing that was attempted
was to call (from libdrm)

	drmModeSetPlane(fd, plane_id, crtc_id, fb_id, 0,
			0, 0, 0, 0, 0, 0, 0, 0);

This call causes a pair of "Division by zero in kernel." messages. Kill
those messages, but preserve the current behaviour that also happen to
make the plane disappear with the above call.

Signed-off-by: Peter Rosin <peda@...ntia.se>
---
 drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

Side note, when comparing with drm_atomic_helper_check_plane_state(), I get
the feeling that the src rect should be clipped together with the crtc rect
if/when clipping is needed. That function calls drm_rect_clip_scaled(), and
the equivalent does not seem to happen here. Should clipping be performed
on the src rect?

Cheers,
Peter

diff --git a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c
index 3cc489b870fe..1bdb30dc218c 100644
--- a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c
+++ b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c
@@ -675,10 +675,16 @@ static int atmel_hlcdc_plane_atomic_check(struct drm_plane *p,
 		state->crtc_y = 0;
 	}
 
-	patched_src_w = DIV_ROUND_CLOSEST(patched_crtc_w * state->src_w,
-					  state->crtc_w);
-	patched_src_h = DIV_ROUND_CLOSEST(patched_crtc_h * state->src_h,
-					  state->crtc_h);
+	if (state->crtc_w)
+		patched_src_w = DIV_ROUND_CLOSEST(patched_crtc_w * state->src_w,
+						  state->crtc_w);
+	else
+		patched_src_w = 0;
+	if (state->crtc_h)
+		patched_src_h = DIV_ROUND_CLOSEST(patched_crtc_h * state->src_h,
+						  state->crtc_h);
+	else
+		patched_src_h = 0;
 
 	hsub = drm_format_horz_chroma_subsampling(fb->format->format);
 	vsub = drm_format_vert_chroma_subsampling(fb->format->format);
-- 
2.11.0