[PATCH 08/12] drm/sun4i: sun6i_mipi_dsi: Refactor vertical video start delay
From: Maxime Ripard <hidden>
Date: 2018-09-27 17:14:57
Also in:
dri-devel, linux-clk, linux-devicetree, lkml
On Thu, Sep 27, 2018 at 05:18:46PM +0530, Jagan Teki wrote:
Accordingly to BPI-M64-bsp DE DSI code Video start delay can be computed by subtracting total vertical timing with front porch timing and with adding 1 delay line for TCON.
This is what the current code is doing as well.
quoted hunk ↗ jump to hunk
This patch simply add the start_delay logic from BPI-M64-bsp, w/o this new computation, the DSI on A64 encounter vblank time out. [CRTC:36:crtc-0] vblank wait timed out Signed-off-by: Jagan Teki <jagan@amarulasolutions.com> --- drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c index 9918fdb990ff..217db74c6dc3 100644 --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c@@ -358,7 +358,17 @@ 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 = mode->vsync_start - mode->vdisplay;
Again, this is wrong and contrary to what your commit log is saying. The Allwinner code has: u32 vfp = panel->lcd_vt - panel->lcd_y - panel->lcd_vbp; u32 dsi_start_delay = panel->lcd_vt - vfp + 1; So, essentially: vtotal - (vtotal - vdisplay - back porch) + 1 The backporch is hsync_total - hsync_end, so we end up, removing the addition / removal of vtotal, with: vdisplay - (vsync_total - vsync_end) + 1 The formula used there looks indeed different, but unlike what you were saying.
+ u32 start_delay; + + start_delay = mode->vtotal - vfp + 1; + if (start_delay > mode->vtotal) + start_delay -= mode->vtotal; + + if (!start_delay) + start_delay = 1; +
I guess that it's actually the clamping that fixes thing. It should be mentionned in your commit log. Maxime -- Maxime Ripard, Bootlin Embedded Linux and Kernel engineering https://bootlin.com