[PATCH v3] drm/sun4i: tcon: fix inverted DCLK polarity

Giulio Benetti
2021-01-11T17:47:44Z

From: Giulio Benetti <giulio.benetti@micronovasrl.com>

During commit 88bc4178568b ("drm: Use new
DRM_BUS_FLAG_*_(DRIVE|SAMPLE)_(POS|NEG)EDGE flags") DRM_BUS_FLAG_*
macros have been changed to avoid ambiguity but just because of this
ambiguity previous DRM_BUS_FLAG_PIXDATA_(POS/NEG)EDGE were used meaning
_SAMPLE_ not _DRIVE_. This leads to DLCK inversion and need to fix but
instead of swapping phase values, let's adopt an easier approach Maxime
suggested:
It turned out that bit 26 of SUN4I_TCON0_IO_POL_REG is dedicated to
invert DCLK polarity and this makes things really easier than before. So
let's handle DCLK polarity by adding SUN4I_TCON0_IO_POL_DCLK_POSITIVE as
bit 26 and activating according to bus_flags the same way it is done for
all the other signals polarity.

Fixes: 88bc4178568b ("drm: Use new DRM_BUS_FLAG_*_(DRIVE|SAMPLE)_(POS|NEG)EDGE flags")
Suggested-by: Maxime Ripard <maxime@cerno.tech>
Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
---
drivers/gpu/drm/sun4i/sun4i_tcon.c | 20 +-------------------
drivers/gpu/drm/sun4i/sun4i_tcon.h | 1 +
2 files changed, 2 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
index eaaf5d70e352..30171ccd87e5 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
@@ -569,26 +569,8 @@ static void sun4i_tcon0_mode_set_rgb(struct sun4i_tcon *tcon,
if (info->bus_flags & DRM_BUS_FLAG_DE_LOW)
val |= SUN4I_TCON0_IO_POL_DE_NEGATIVE;

- /*
- * 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 (info->bus_flags & DRM_BUS_FLAG_PIXDATA_DRIVE_POSEDGE)
- clk_set_phase(tcon->dclk, 240);
-
- if (info->bus_flags & DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE)
- clk_set_phase(tcon->dclk, 0);
+ val |= SUN4I_TCON0_IO_POL_DCLK_POSITIVE;

regmap_update_bits(tcon->regs, SUN4I_TCON0_IO_POL_REG,
SUN4I_TCON0_IO_POL_HSYNC_POSITIVE |
diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.h b/drivers/gpu/drm/sun4i/sun4i_tcon.h
index cfbf4e6c1679..0ce71d10a31b 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.h
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.h
@@ -113,6 +113,7 @@
#define SUN4I_TCON0_IO_POL_REG 0x88
#define SUN4I_TCON0_IO_POL_DCLK_PHASE(phase) ((phase & 3) << 28)
#define SUN4I_TCON0_IO_POL_DE_NEGATIVE BIT(27)
+#define SUN4I_TCON0_IO_POL_DCLK_POSITIVE BIT(26)
#define SUN4I_TCON0_IO_POL_HSYNC_POSITIVE BIT(25)
#define SUN4I_TCON0_IO_POL_VSYNC_POSITIVE BIT(24)

--
2.25.1