linux-kernel - [PATCH v1] drm/mediatek: fix up 1440x900 dp display black screen issue

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Date:   Tue, 26 Nov 2019 14:47:49 +0800
From:   <yongqiang.niu@...iatek.com>
To:     CK Hu <ck.hu@...iatek.com>, Philipp Zabel <p.zabel@...gutronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>
CC:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Mark Rutland <mark.rutland@....com>,
        <dri-devel@...ts.freedesktop.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>,
        Yongqiang Niu <yongqiang.niu@...iatek.com>
Subject: [PATCH v1] drm/mediatek: fix up 1440x900 dp display black screen issue

From: Yongqiang Niu <yongqiang.niu@...iatek.com>

This patch fix up 1440x900 dp display black screen issue
the computed result will overflow rdma1 fifo max size
when external display pixel clock bigger than 74MHZ

Signed-off-by: Yongqiang Niu <yongqiang.niu@...iatek.com>
---
 drivers/gpu/drm/mediatek/mtk_disp_rdma.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/mediatek/mtk_disp_rdma.c b/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
index c1abde3..41143f5 100644
--- a/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
+++ b/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
@@ -152,6 +152,10 @@ static void mtk_rdma_config(struct mtk_ddp_comp *comp, unsigned int width,
 	 * account for blanking, and with a pixel depth of 4 bytes:
 	 */
 	threshold = width * height * vrefresh * 4 * 7 / 1000000;
+
+	if (threshold > rdma_fifo_size)
+		threshold = rdma_fifo_size;
+
 	reg = RDMA_FIFO_UNDERFLOW_EN |
 	      RDMA_FIFO_PSEUDO_SIZE(rdma_fifo_size) |
 	      RDMA_OUTPUT_VALID_FIFO_THRESHOLD(threshold);
-- 
1.8.1.1.dirty