Handle both positive and negative dclk polarity,
according to bus_flags, taking care of this:
On A20 and similar SoCs, the only way to achieve Positive Edge
(Rising Edge), is setting dclk clock phase to 2/3(240°).
By default TCON works in Negative Edge(Falling Edge), this is why phase
is set to 0 in that case.
Unfortunately there's no way to logically invert dclk through IO_POL
register.
The only acceptable way to work, triple checked with scope,
is using clock phase set to 0° for Negative Edge and set to 240° for
Positive Edge.
On A33 and similar SoCs there would be a 90° phase option, but it divides
also dclk by 2.
This patch is a way to avoid quirks all around TCON and DOTCLOCK drivers
for using A33 90° phase divided by 2 and consequently increase code
complexity.
Signed-off-by: Giulio Benetti <giulio.benetti@xxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/sun4i/sun4i_tcon.c | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)
diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
index 8ee87c2..3f1455d 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
@@ -17,6 +17,7 @@
#include <drm/drm_encoder.h>
#include <drm/drm_modes.h>
#include <drm/drm_of.h>
+#include <drm/drm_panel.h>
#include <uapi/drm/drm_mode.h>
@@ -345,6 +346,9 @@ static void sun4i_tcon0_mode_set_lvds(struct sun4i_tcon *tcon,
static void sun4i_tcon0_mode_set_rgb(struct sun4i_tcon *tcon,
const struct drm_display_mode *mode)
{
+ struct drm_panel *panel = tcon->panel;
+ struct drm_connector *connector = panel->connector;
+ struct drm_display_info display_info = connector->display_info;
unsigned int bp, hsync, vsync;
u8 clk_delay;
u32 val = 0;
@@ -400,6 +404,27 @@ static void sun4i_tcon0_mode_set_rgb(struct sun4i_tcon *tcon,
if (mode->flags & DRM_MODE_FLAG_PVSYNC)
val |= SUN4I_TCON0_IO_POL_VSYNC_POSITIVE;
+ /*
+ * On A20 and similar SoCs, the only way to achieve Positive Edge
+ * (Rising Edge), is setting dclk clock phase to 2/3(240°).
+ * By default TCON works in Negative Edge(Falling Edge),
+ * this is why phase is set to 0 in that case.
+ * Unfortunately there's no way to logically invert dclk through
+ * IO_POL register.
+ * The only acceptable way to work, triple checked with scope,
+ * is using clock phase set to 0° for Negative Edge and set to 240°
+ * for Positive Edge.
+ * On A33 and similar SoCs there would be a 90° phase option,
+ * but it divides also dclk by 2.
+ * Following code is a way to avoid quirks all around TCON
+ * and DOTCLOCK drivers.
+ */
+ if (display_info.bus_flags & DRM_BUS_FLAG_PIXDATA_POSEDGE)
+ clk_set_phase(tcon->dclk, 240);
+
+ if (display_info.bus_flags & DRM_BUS_FLAG_PIXDATA_NEGEDGE)
+ clk_set_phase(tcon->dclk, 0);
+
regmap_update_bits(tcon->regs, SUN4I_TCON0_IO_POL_REG,
SUN4I_TCON0_IO_POL_HSYNC_POSITIVE | SUN4I_TCON0_IO_POL_VSYNC_POSITIVE,
val);
--
2.7.4
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