drm/mediatek: dsi: Modify horizontal front/back porch byte formula

In the patch to be fixed, horizontal_backporch_byte become too large
for some panel, so roll back that patch. For small hfp or hbp panel,
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.hu@mediatek.com>
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Tested-by: Bilal Wasim <bilal.wasim@imgtec.com>

diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c b/drivers/gpu/drm/mediatek/mtk_dsi.c
index 4a188a9..65fd99c 100644 (file)
--- 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;
@@ -466,50 +469,30 @@ static void mtk_dsi_config_vdo_timing(struct mtk_dsi *dsi)
        horizontal_sync_active_byte = (vm->hsync_len * dsi_tmp_buf_bpp - 10);
 
        if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO_SYNC_PULSE)
-               horizontal_backporch_byte = vm->hback_porch * dsi_tmp_buf_bpp;
+               horizontal_backporch_byte = vm->hback_porch * dsi_tmp_buf_bpp - 10;
        else
                horizontal_backporch_byte = (vm->hback_porch + vm->hsync_len) *
-                                           dsi_tmp_buf_bpp;
+                                           dsi_tmp_buf_bpp - 10;
 
        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;
-               }
+                         timing->da_hs_zero + timing->da_hs_exit + 3;
+
+       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);