Re: [PATCH v5 1/1] drm/mediatek: dsi: fix scrolling of panel with small hfp or hbp

[Nicolas Boichat <drinkcat@chromium.org>]

On Tue, Oct 13, 2020 at 6:06 PM Jitao Shi <jitao.shi@mediatek.com> wrote:
>
> 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.shi@mediatek.com>
> ---
>  drivers/gpu/drm/mediatek/mtk_dsi.c | 65 +++++++++++++++-----------------------
>  1 file changed, 25 insertions(+), 40 deletions(-)
>
> diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c b/drivers/gpu/drm/mediatek/mtk_dsi.c
> index 80b7a082e874..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;
> @@ -466,50 +467,34 @@ 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);

These parentheses are not required, but it might be a little clearer to write:
(vm->hback_porch * dsi_tmp_buf_bpp) - 10;

>         else
> -               horizontal_backporch_byte = (vm->hback_porch + vm->hsync_len) *
> -                                           dsi_tmp_buf_bpp;
> +               horizontal_backporch_byte = ((vm->hback_porch + vm->hsync_len) *
> +                       dsi_tmp_buf_bpp - 10);

ditto:
((vm->hback_porch + vm->hsync_len) * dsi_tmp_buf_bpp) - 10;

But then, _maybe_ it's clearer to drop this hunk and just add this
below the if/else:

horizontal_backporch_byte -= 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;

(for reference, apart from this `+ 3`, there is no functional change
in this hunk: this just moves delta outside of the if/else block,
which is a good idea for readability)

> +
> +       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
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