[PATCH v4] drm/mgag200: Apply upper limit for clock variable

[Murad Masimov]

If the value of the clock variable is higher than 800000, the value of the
variable m, which is used as a divisor, will remain zero, because
(clock * testp) will be higher than vcomax in every loop iteration, which
leads to skipping every iteration and leaving variable m unmodified.

Return -EINVAL just after the loop, if m is still 0.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 877507bb954e ("drm/mgag200: Provide per-device callbacks for PIXPLLC")
Signed-off-by: Murad Masimov <m.masimov at mt-integration.ru>
Reviewed-by: Jocelyn Falempe <jfalempe at redhat.com>
---
 drivers/gpu/drm/mgag200/mgag200_g200se.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/mgag200/mgag200_g200se.c b/drivers/gpu/drm/mgag200/mgag200_g200se.c
index 7a32d3b1d226..4d65ead63d66 100644
--- a/drivers/gpu/drm/mgag200/mgag200_g200se.c
+++ b/drivers/gpu/drm/mgag200/mgag200_g200se.c
@@ -249,6 +249,9 @@ static int mgag200_g200se_04_pixpllc_atomic_check(struct drm_crtc *crtc,
 		}
 	}

+	if (m == 0)
+		return -EINVAL;
+
 	fvv = pllreffreq * n / m;
 	fvv = (fvv - 800000) / 50000;
 	if (fvv > 15)
--
2.39.2