[PATCH v4 2/2] drm/mediatek: dsi: fix scrolling of panel with small hfp or hbp

[Jitao Shi]

Replace horizontal_backporch_byte with vm->hback_porch * bpp to aovid
flowing judgement negative number.

if ((vm->hfront_porch * dsi_tmp_buf_bpp + horizontal_backporch_byte) >
        data_phy_cycles * dsi->lanes + delta)

Signed-off-by: Jitao Shi <jitao....@mediatek.com>
---
 drivers/gpu/drm/mediatek/mtk_dsi.c | 54 ++++++++++++++------------------------
 1 file changed, 19 insertions(+), 35 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c 
b/drivers/gpu/drm/mediatek/mtk_dsi.c
index 16fd99dcdacf..ddddf69ebeaf 100644
--- a/drivers/gpu/drm/mediatek/mtk_dsi.c
+++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
@@ -445,6 +445,7 @@ static void mtk_dsi_config_vdo_timing(struct mtk_dsi *dsi)
        u32 horizontal_backporch_byte;
        u32 horizontal_frontporch_byte;
        u32 dsi_tmp_buf_bpp, data_phy_cycles;
+       u32 delta;
        struct mtk_phy_timing *timing = &dsi->phy_timing;
 
        struct videomode *vm = &dsi->vm;
@@ -475,42 +476,25 @@ 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 + 3;
 
-       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;
+
+       if ((vm->hfront_porch * dsi_tmp_buf_bpp + horizontal_backporch_byte) >
+           data_phy_cycles * dsi->lanes + delta) {
+               horizontal_frontporch_byte =
+                       vm->hfront_porch * dsi_tmp_buf_bpp -
+                       (data_phy_cycles * dsi->lanes + delta) *
+                       vm->hfront_porch /
+                       (vm->hfront_porch + vm->hback_porch);
+
+               horizontal_backporch_byte =
+                       horizontal_backporch_byte -
+                       (data_phy_cycles * dsi->lanes + delta) *
+                       vm->hback_porch /
+                       (vm->hfront_porch + vm->hback_porch);
        } 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");
+               horizontal_frontporch_byte = vm->hfront_porch *
+                                            dsi_tmp_buf_bpp;
        }
 
        writel(horizontal_sync_active_byte, dsi->regs + DSI_HSA_WC);
-- 
2.12.5