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From:   Jagan Teki <jagan@amarulasolutions.com>
To:     Maxime Ripard <maxime.ripard@bootlin.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>, Chen-Yu Tsai <wens@csie.org>
Cc:     michael@amarulasolutions.com, linux-amarula@amarulasolutions.com,
        dri-devel@lists.freedesktop.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-sunxi@googlegroups.com,
        Jagan Teki <jagan@amarulasolutions.com>
Subject: [PATCH v10 1/2] drm/sun4i: sun6i_mipi_dsi: Fix hsync_porch overflow
Date:   Mon, 13 May 2019 00:11:26 +0530
Message-Id: <20190512184128.13720-2-jagan@amarulasolutions.com>
In-Reply-To: <20190512184128.13720-1-jagan@amarulasolutions.com>
References: <20190512184128.13720-1-jagan@amarulasolutions.com>
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Loop N1 instruction delay for burst mode devices are computed
based on horizontal sync and porch timing values.

The current driver is using u16 type for computing this hsync_porch
value, which would failed to fit within the u16 type for large sync
and porch timings devices. This would result in hsync_porch overflow
and eventually computed wrong instruction delay value.

Example, timings, where it produces the overflow
{
	.hdisplay       = 1080,
	.hsync_start    = 1080 + 408,
        .hsync_end      = 1080 + 408 + 4,
        .htotal         = 1080 + 408 + 4 + 38,
}

It reproduces the desired delay value 65487 but the correct working
value should be 7.

So, Fix it by computing hsync_porch value separately with u32 type.

Fixes: 1c1a7aa3663c ("drm/sun4i: dsi: Add burst support")
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
---
 drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
index 6ff585055a07..bfa7e2b146df 100644
--- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
+++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
@@ -457,8 +457,9 @@ static void sun6i_dsi_setup_inst_loop(struct sun6i_dsi *dsi,
 	u16 delay = 50 - 1;
 
 	if (device->mode_flags & MIPI_DSI_MODE_VIDEO_BURST) {
-		delay = (mode->htotal - mode->hdisplay) * 150;
-		delay /= (mode->clock / 1000) * 8;
+		u32 hsync_porch = (mode->htotal - mode->hdisplay) * 150;
+
+		delay = (hsync_porch / ((mode->clock / 1000) * 8));
 		delay -= 50;
 	}
 
-- 
2.18.0.321.gffc6fa0e3