On Wed, Jan 30, 2019 at 11:23 AM Chen-Yu Tsai wens@csie.org wrote:
On Wed, Jan 23, 2019 at 11:54 PM Maxime Ripard maxime.ripard@bootlin.com wrote:
The current calculation for the video start delay in the current DSI driver is that it is the total vertical size, minus the backporch and sync length, plus 1.
However, the Allwinner code has it as the active vertical size, plus the back porch and the sync length. This doesn't make any difference on the only panel it has been tested with so far, since in that particular case the front porch is equal to the sum of the back porch and sync length.
This is not the case for all panels, obviously, so we need to fix it. Since the Allwinner code has a bunch of extra code to deal with out of bounds values, so let's add them as well.
Signed-off-by: Maxime Ripard maxime.ripard@bootlin.com
drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c index 380fc527a707..e3e4ba90c059 100644 --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c @@ -357,7 +357,12 @@ 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;According to the diagram in include/drm/drm_modes.h , This is active region plus back porch plus 1, as
sync_end - display = length of front porch and sync
u16 delay = (mode->vsync_end + 1) % mode->vtotal;And this actually means
(length of active region and front porch and sync pulse plus 1) %total length
So I don't really understand what's happening here. And the modulus is unexplained.
Attempting to make sense of this. Allwinner's A64 BSP the following which uses their definitions for y, vbp, vt:
s32 start_delay = panel->lcd_vt - panel->lcd_y -10; u32 vfp = panel->lcd_vt - panel->lcd_y - panel->lcd_vbp; u32 dsi_start_delay;
/* put start_delay to tcon. set ready sync early to dramfreq, so set start_delay 1 */ start_delay = 1;
dsi_start_delay = panel->lcd_vt - vfp + start_delay; if (dsi_start_delay > panel->lcd_vt) dsi_start_delay -= panel->lcd_vt; if (dsi_start_delay==0) dsi_start_delay = 1;
This can be converted to
dsi_start_delay = max(1, (mode->vtotal - (mode->vtotal - mode->vdisplay - (mode->vtotal - mode->vsync_start)) + 1) % mode->vtotal)
and simplified to
dsi_start_delay = max(1, (mode->vtotal + mode->vdisplay - mode->vsync_start) + 1) % mode->vtotal)
and reordered to the following
dsi_start_delay = max(1, (mode->vtotal - (mode->vsync_start - mode->vdisplay) + 1) % mode->vtotal)
which means total length minus front porch, or length of active portion plus back porch plus sync. Based on your commit message, the last derivation is what you want.
ChenYu
if (!delay)delay = 1;Same comment as Paul.
ChenYu
return delay;}
static void sun6i_dsi_setup_burst(struct sun6i_dsi *dsi,
git-series 0.9.1
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