From mboxrd@z Thu Jan 1 00:00:00 1970 From: Maxime Ripard Subject: Re: [PATCH 08/12] drm/sun4i: sun6i_mipi_dsi: Refactor vertical video start delay Date: Thu, 27 Sep 2018 19:14:51 +0200 Message-ID: <20180927171451.7iqt2nt2log5qojf@flea> References: <20180927114850.24565-1-jagan@amarulasolutions.com> <20180927114850.24565-9-jagan@amarulasolutions.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8BIT Return-path: Content-Disposition: inline In-Reply-To: <20180927114850.24565-9-jagan@amarulasolutions.com> Sender: linux-kernel-owner@vger.kernel.org To: Jagan Teki Cc: Chen-Yu Tsai , Icenowy Zheng , Jernej Skrabec , Vasily Khoruzhick , Rob Herring , Mark Rutland , Catalin Marinas , Will Deacon , David Airlie , dri-devel@lists.freedesktop.org, Michael Turquette , Stephen Boyd , linux-clk@vger.kernel.org, Michael Trimarchi , linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-sunxi@googlegroups.com List-Id: devicetree@vger.kernel.org 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. > 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 > --- > 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