linux-kernel - [PATCH 2/3] drm/sun4i: dsi: fix DRQ calculation

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Message-Id: <20191001080253.6135-3-icenowy@aosc.io>
Date:   Tue,  1 Oct 2019 16:02:52 +0800
From:   Icenowy Zheng <icenowy@...c.io>
To:     Maxime Ripard <mripard@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...glegroups.com, Icenowy Zheng <icenowy@...c.io>
Subject: [PATCH 2/3] drm/sun4i: dsi: fix DRQ calculation

According to the BSP source code, when calculating the magic DRQ value
outside burst mode, a formula of "lcd_ht - lcd_x - lcd_hbp", which is
interpreted as right margin (HFP value). However, currently the
sun6i_mipi_dsi driver code calculates it wrongly as HFP + sync length,
which lead to timing error.

Fix the DRQ calculation by change it to use HFP.

Signed-off-by: Icenowy Zheng <icenowy@...c.io>
---
 drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
index c86e11631ebc..2d3e822a7739 100644
--- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
+++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
@@ -436,9 +436,9 @@ static void sun6i_dsi_setup_burst(struct sun6i_dsi *dsi,
 			     SUN6I_DSI_BURST_LINE_SYNC_POINT(SUN6I_DSI_SYNC_POINT));
 
 		val = SUN6I_DSI_TCON_DRQ_ENABLE_MODE;
-	} else if ((mode->hsync_end - mode->hdisplay) > 20) {
+	} else if ((mode->hsync_start - mode->hdisplay) > 20) {
 		/* Maaaaaagic */
-		u16 drq = (mode->hsync_end - mode->hdisplay) - 20;
+		u16 drq = (mode->hsync_start - mode->hdisplay) - 20;
 
 		drq *= mipi_dsi_pixel_format_to_bpp(device->format);
 		drq /= 32;
-- 
2.21.0