[PATCH] drm/mediatek: dsi: Calculate horizontal_backporch_byte by itself

[Chun-Kuang Hu]

From: CK Hu <ck...@mediatek.com>

Using vm->hfront_porch + vm->hback_porch to calculate
horizontal_backporch_byte would make it negtive, so
use horizontal_backporch_byte itself to make it positive.

Fixes: 35bf948f1edb ("drm/mediatek: dsi: Fix scrolling of panel with small hfp 
or hbp")

Signed-off-by: CK Hu <ck...@mediatek.com>
Signed-off-by: Chun-Kuang Hu <chunkuang...@kernel.org>
---
 drivers/gpu/drm/mediatek/mtk_dsi.c | 53 ++++++++++--------------------
 1 file changed, 18 insertions(+), 35 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c 
b/drivers/gpu/drm/mediatek/mtk_dsi.c
index 4a188a942c38..2a64fdaed9a7 100644
--- a/drivers/gpu/drm/mediatek/mtk_dsi.c
+++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
@@ -444,7 +444,10 @@ static void mtk_dsi_config_vdo_timing(struct mtk_dsi *dsi)
        u32 horizontal_sync_active_byte;
        u32 horizontal_backporch_byte;
        u32 horizontal_frontporch_byte;
+       u32 horizontal_front_back_byte;
+       u32 data_phy_cycles_byte;
        u32 dsi_tmp_buf_bpp, data_phy_cycles;
+       u32 delta;
        struct mtk_phy_timing *timing = &dsi->phy_timing;
 
        struct videomode *vm = &dsi->vm;
@@ -474,42 +477,22 @@ static void mtk_dsi_config_vdo_timing(struct mtk_dsi *dsi)
        data_phy_cycles = timing->lpx + timing->da_hs_prepare +
                          timing->da_hs_zero + timing->da_hs_exit;
 
-       if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO_BURST) {
-               if ((vm->hfront_porch + vm->hback_porch) * dsi_tmp_buf_bpp >
-                   data_phy_cycles * dsi->lanes + 18) {
-                       horizontal_frontporch_byte =
-                               vm->hfront_porch * dsi_tmp_buf_bpp -
-                               (data_phy_cycles * dsi->lanes + 18) *
-                               vm->hfront_porch /
-                               (vm->hfront_porch + vm->hback_porch);
-
-                       horizontal_backporch_byte =
-                               horizontal_backporch_byte -
-                               (data_phy_cycles * dsi->lanes + 18) *
-                               vm->hback_porch /
-                               (vm->hfront_porch + vm->hback_porch);
-               } else {
-                       DRM_WARN("HFP less than d-phy, FPS will under 60Hz\n");
-                       horizontal_frontporch_byte = vm->hfront_porch *
-                                                    dsi_tmp_buf_bpp;
-               }
+       delta = dsi->mode_flags & MIPI_DSI_MODE_VIDEO_BURST ? 18 : 12;
+
+       horizontal_frontporch_byte = vm->hfront_porch * dsi_tmp_buf_bpp;
+       horizontal_front_back_byte = horizontal_frontporch_byte + 
horizontal_backporch_byte;
+       data_phy_cycles_byte = data_phy_cycles * dsi->lanes + delta;
+
+       if (horizontal_front_back_byte > data_phy_cycles_byte) {
+               horizontal_frontporch_byte -= data_phy_cycles_byte *
+                                             horizontal_frontporch_byte /
+                                             horizontal_front_back_byte;
+
+               horizontal_backporch_byte -= data_phy_cycles_byte *
+                                            horizontal_backporch_byte /
+                                            horizontal_front_back_byte;
        } else {
-               if ((vm->hfront_porch + vm->hback_porch) * dsi_tmp_buf_bpp >
-                   data_phy_cycles * dsi->lanes + 12) {
-                       horizontal_frontporch_byte =
-                               vm->hfront_porch * dsi_tmp_buf_bpp -
-                               (data_phy_cycles * dsi->lanes + 12) *
-                               vm->hfront_porch /
-                               (vm->hfront_porch + vm->hback_porch);
-                       horizontal_backporch_byte = horizontal_backporch_byte -
-                               (data_phy_cycles * dsi->lanes + 12) *
-                               vm->hback_porch /
-                               (vm->hfront_porch + vm->hback_porch);
-               } else {
-                       DRM_WARN("HFP less than d-phy, FPS will under 60Hz\n");
-                       horizontal_frontporch_byte = vm->hfront_porch *
-                                                    dsi_tmp_buf_bpp;
-               }
+               DRM_WARN("HFP + HBP less than d-phy, FPS will under 60Hz\n");
        }
 
        writel(horizontal_sync_active_byte, dsi->regs + DSI_HSA_WC);
-- 
2.17.1