linux-kernel - Re: [PATCH v8 7/8] drm/sun4i: sun6i_mipi_dsi: Refactor vertical video start delay

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Message-ID: <CAMty3ZDqnVBkcT5kiKf-pKGccEuQR0xtBXBgB2-_XFXkRKi+_A@mail.gmail.com>
Date:   Sat, 16 Feb 2019 01:07:08 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, Chen-Yu Tsai <wens@...e.org>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-amarula@...rulasolutions.com,
        Michael Trimarchi <michael@...rulasolutions.com>
Subject: Re: [PATCH v8 7/8] drm/sun4i: sun6i_mipi_dsi: Refactor vertical video
 start delay

On Fri, Feb 15, 2019 at 12:56 AM Jagan Teki <jagan@...rulasolutions.com> wrote:
>
> Vertical video start delay is computed by excluding vertical porch
> value from total vertical timings, but the current driver excluding
> vertical porch along with vertical sync values from total vertical
> timings resulting wrong start delay.
>
> This patch trying to update the video start delay by subtracting
> vertical porch from vertical total, on the other hand it added 1
> extra start_delay line for TCON based on the Allwinner BSP reference.
>
> BSP code form BPI-M64-bsp is computing video start delay as
> (from linux-sunxi/
> drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/de_dsi.c)
>
> u32 vfp = panel->lcd_vt - panel->lcd_y - panel->lcd_vbp;
> => (panel->lcd_vt) - panel->lcd_y - (panel->lcd_vbp)
> => (timmings->ver_front_porch + panel->lcd_vbp + panel->lcd_y)
>    - panel->lcd_y - (panel->lcd_vbp)
> => timmings->ver_front_porch + panel->lcd_vbp + panel->lcd_y
>                              - panel->lcd_y - panel->lcd_vbp
> => timmings->ver_front_porch
>
> So, update the start delay computation accordingly.
>
> Signed-off-by: Jagan Teki <jagan@...rulasolutions.com>
> ---
>  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> index a08dfdcbe9e8..31cf9c58e98d 100644
> --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> @@ -358,7 +358,24 @@ static void sun6i_dsi_inst_init(struct sun6i_dsi *dsi,
>  static u16 sun6i_dsi_get_video_start_delay(struct sun6i_dsi *dsi,
>                                            struct drm_display_mode *mode)
>  {
> -       return mode->vtotal - (mode->vsync_end - mode->vdisplay) + 1;
> +       u32 vfp, start_delay;
> +
> +       /* vertical front porch */
> +       vfp = mode->vsync_start - mode->vdisplay;
> +
> +       /* start_delay = vertical total - vertical front porch */
> +       start_delay = mode->vtotal - vfp;
> +
> +       /* add extra 1 delay line for TCON, as per Allwinner BSP */
> +       start_delay = 1;

This has to be += 1;

Typo change while re-basing, I will fix this in next version.