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Message-ID: <3972834.uPFdDeCNB3@kista> Date: Fri, 05 Feb 2021 19:47:17 +0100 From: Jernej Škrabec <jernej.skrabec@...l.net> To: Chen-Yu Tsai <wens@...e.org> Cc: Maxime Ripard <maxime@...no.tech>, Mike Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>, linux-clk <linux-clk@...r.kernel.org>, linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, linux-kernel <linux-kernel@...r.kernel.org>, dri-devel <dri-devel@...ts.freedesktop.org>, linux-sunxi <linux-sunxi@...glegroups.com>, Andre Heider <a.heider@...il.com> Subject: Re: Re: Re: [PATCH 2/5] drm/sun4i: tcon: set sync polarity for tcon1 channel Dne petek, 05. februar 2021 ob 17:28:23 CET je Chen-Yu Tsai napisal(a): > On Sat, Feb 6, 2021 at 12:21 AM Jernej Škrabec <jernej.skrabec@...l.net> wrote: > > > > Dne petek, 05. februar 2021 ob 17:01:30 CET je Maxime Ripard napisal(a): > > > On Fri, Feb 05, 2021 at 11:21:22AM +0800, Chen-Yu Tsai wrote: > > > > On Fri, Feb 5, 2021 at 2:48 AM Jernej Skrabec <jernej.skrabec@...l.net> > > wrote: > > > > > > > > > > Channel 1 has polarity bits for vsync and hsync signals but driver never > > > > > sets them. It turns out that with pre-HDMI2 controllers seemingly there > > > > > is no issue if polarity is not set. However, with HDMI2 controllers > > > > > (H6) there often comes to de-synchronization due to phase shift. This > > > > > causes flickering screen. It's safe to assume that similar issues might > > > > > happen also with pre-HDMI2 controllers. > > > > > > > > > > Solve issue with setting vsync and hsync polarity. Note that display > > > > > stacks with tcon top have polarity bits actually in tcon0 polarity > > > > > register. > > > > > > > > > > Fixes: 9026e0d122ac ("drm: Add Allwinner A10 Display Engine support") > > > > > Tested-by: Andre Heider <a.heider@...il.com> > > > > > Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net> > > > > > --- > > > > > drivers/gpu/drm/sun4i/sun4i_tcon.c | 24 ++++++++++++++++++++++++ > > > > > drivers/gpu/drm/sun4i/sun4i_tcon.h | 5 +++++ > > > > > 2 files changed, 29 insertions(+) > > > > > > > > > > diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/ sun4i/ > > sun4i_tcon.c > > > > > index 6b9af4c08cd6..0d132dae58c0 100644 > > > > > --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c > > > > > +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c > > > > > @@ -672,6 +672,29 @@ static void sun4i_tcon1_mode_set(struct sun4i_tcon > > *tcon, > > > > > SUN4I_TCON1_BASIC5_V_SYNC(vsync) | > > > > > SUN4I_TCON1_BASIC5_H_SYNC(hsync)); > > > > > > > > > > + /* Setup the polarity of sync signals */ > > > > > + if (tcon->quirks->polarity_in_ch0) { > > > > > + val = 0; > > > > > + > > > > > + if (mode->flags & DRM_MODE_FLAG_PHSYNC) > > > > > + val |= SUN4I_TCON0_IO_POL_HSYNC_POSITIVE; > > > > > + > > > > > + if (mode->flags & DRM_MODE_FLAG_PVSYNC) > > > > > + val |= SUN4I_TCON0_IO_POL_VSYNC_POSITIVE; > > > > > + > > > > > + regmap_write(tcon->regs, SUN4I_TCON0_IO_POL_REG, val); > > > > > + } else { > > > > > + val = SUN4I_TCON1_IO_POL_UNKNOWN; > > > > > > > > I think a comment for the origin of this is warranted. > > > > > > If it's anything like TCON0, it's the pixel clock polarity > > > > Hard to say, DW HDMI controller has "data enable" polarity along hsync and > > vsync. It could be either or none of those. > > > > What should I write in comment? BSP drivers and documentation use only generic > > names like io2_inv. > > Just say that we don't know exactly what it is, but it is required for things > to work properly? Would be interesting to know what happens if you don't set > this bit, but do set VSYNC/HSYNC polarity properly. Nothing seems to happen - tested on H3 with HDMI (4k@30) and CVBS. At least I didn't notice anything. Best regards, Jernej
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