linux-kernel - [PATCH v10 1/2] drm/sun4i: sun6i_mipi_dsi: Fix hsync

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Date:   Mon, 13 May 2019 00:11:26 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, Chen-Yu Tsai <wens@...e.org>
Cc:     michael@...rulasolutions.com, linux-amarula@...rulasolutions.com,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...glegroups.com,
        Jagan Teki <jagan@...rulasolutions.com>
Subject: [PATCH v10 1/2] drm/sun4i: sun6i_mipi_dsi: Fix hsync_porch overflow

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@...rulasolutions.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