Re: [PATCH 2/5] drm/sun4i: tcon: set sync polarity for tcon1 channel
From: Maxime Ripard <hidden>
Date: 2021-02-05 23:26:26
Also in:
dri-devel, linux-clk, lkml
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 [off-list ref] wrote:quoted
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 <redacted> Signed-off-by: Jernej Skrabec <redacted> --- 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 Maxime _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel