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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Maxime, On Fri, Feb 8, 2019 at 3:23 PM Maxime Ripard wrote: > > The current calculation for the video start delay in the current DSI driver > is that it is the total vertical size, minus the front porch and sync length, > plus 1. This equals to the active vertical size plus the back porch plus 1. > > That 1 is coming in the Allwinner BSP from an variable that is set to 1. > However, if we look at the Allwinner BSP more closely, and especially in > the "legacy" code for the display (in drivers/video/sunxi/legacy/), we can > see that this variable is actually computed from the porches and the sync > minus 10, clamped between 8 and 100. > > This fixes the start delay symptom we've seen on some panels (vblank > timeouts with vertical white stripes at the bottom of the panel). > > Signed-off-by: Maxime Ripard > --- > drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 4 +++- > 1 file changed, 3 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..9471fa695ec7 100644 > --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c > +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c > @@ -357,7 +357,9 @@ 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; > + u16 start = clamp(mode->vtotal - mode->vdisplay - 10, 8, 100); > + > + return mode->vtotal - (mode->vsync_end - mode->vdisplay) + start; > } As you stated in commit message about result as "active vertical size + Back porch" which indeed correct in reverse way of previous code. but the change seems incorrect to me. => mode->vtotal - (mode->vsync_end - mode->vdisplay) + start => mode->vtotal - (mode->vsync_end - mode->vdisplay) + (mode->vtotal - mode->vdisplay) # bypass 10 for now => mode->vtotal - mode->vsync_end + mode->vdisplay + mode->vtotal - mode->vdisplay => (mode->vtotal - mode->vsync_end) + mode->vtotal => Back porch + mode->vtotal but not => Back porch + mode->vdisplay Let me know if I'm wrong? _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel