Re: [PATCH v8 01/15] drm/sun4i: dsi: Fix video start delay computation
From: Maxime Ripard
Date: Mon Mar 11 2019 - 11:37:43 EST
On Mon, Mar 11, 2019 at 07:06:23PM +0530, Jagan Teki wrote:
> Vertical video start delay is computed by excluding vertical front
> porch value from total vertical timings.
> This clearly confirmed from BSP code and here how it computed,
> 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
> But the current driver is assuming it can exclude vertical front
> porch along with vertical sync values from total vertical timings,
> which resulting wrong start delay indeed wrong picture rendering
> in the panel.
Same story here: which panel, which datasheet, which "wrong picture
> Example: timings, where it produces the issue.
> .vdisplay = 600,
> .vsync_start = 600 + 12,
> .vsync_end = 600 + 12 + 2,
> .vtotal = 600 + 12 + 2 + 21,
Can you 100% trust those timings?
> It produces the desired start delay value as 19 but the correct working
> value should be 513.
> So, Fix it by computing proper video start delay.
> Fixes: 69006ef0ecb1 ("drm/sun4i: dsi: Change the start delay calculation")
> Signed-off-by: Jagan Teki <jagan@xxxxxxxxxxxxxxxxxxxx>
> drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
> diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> index 62a508420227..8d6292c0158b 100644
> --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> @@ -364,8 +364,14 @@ 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)
> - u16 start = clamp(mode->vtotal - mode->vdisplay - 10, 8, 100);
> - u16 delay = mode->vtotal - (mode->vsync_end - mode->vdisplay) + start;
> + u16 delay = mode->vtotal - (mode->vsync_start - mode->vdisplay);
> + /**
> + * BSP comment:
> + * put start_delay to tcon. set ready sync early to dramfreq,
> + * so set start_delay 1
> + */
That doesn't make any sense to me... What does it mean?
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
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