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

[Chun-Kuang Hu <chunkuang.hu@kernel.org>]

Hi, Jitao:

Jitao Shi <jitao.shi@mediatek.com> 於 2020年10月13日 週二 下午6:06寫道：
>
> 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);
>         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);
>
>         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;
> +
> +       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;

I've applied this patch, but small hbp has problem because
horizontal_backporch_byte < 0.
I try to modify this patch according to two assumption:

1. horizontal_backporch_byte should be smaller than (vm->hback_porch +
vm->hsync_len) * dsi_tmp_buf_bpp at least 10.
2. horizontal_backporch_byte should >= 0.

According to these two assumption, I've a patch [1]. My key point is
that I use horizontal_backporch_byte to calculate the ratio to
subtract it. Is my assumption correct?
If not, please explain why do you calculate in this way, so we could
find out how to solve this problem.

[1] https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/2506992

Regards,
Chun-Kuang.

>         }
>
>         writel(horizontal_sync_active_byte, dsi->regs + DSI_HSA_WC);
> --
> 2.12.5
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