Re: [PATCH v6] drm/sun4i: tcon: fix inverted DCLK polarity

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Hello,

Tested on a13 and works.

Here are results:

with DRIVE_NEGEDGE

https://pasteboard.co/JJAGDAy.jpg

https://pasteboard.co/JJAHDAj.jpg

with DRIVE_POSEDGE

https://pasteboard.co/JJAIbBf.jpg

https://pasteboard.co/JJAIGfo.jpg


Il 14/01/2021 09:17, Giulio Benetti ha scritto:
From: Giulio Benetti <giulio.benetti@xxxxxxxxxxxxxxxx>

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_DRIVE_NEGEDGE
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@xxxxxxxxxx>
Signed-off-by: Giulio Benetti <giulio.benetti@xxxxxxxxxxxxxxxx>

Tested-by: Marjan Pascolo <marjan.pascolo@xxxxxxxxx>
[Tested successfully with A13]

---
V2->V3:
- squash 2 patches into 1
V3->V4:
- add SUN4I_TCON0_IO_POL_DCLK_POSITIVE to regmap_update_bits() as suggested by Maxime
V4->V5:
polarity is still wrong so:
- let's use SUN4I_TCON0_IO_POL_DCLK_DRIVE_NEGEDGE macro
   instead of _DCLK_POSITIVE(that would make sense only in realtion with DCLK)
- invert condition using _NEGEDGE instead of _POSEDGE and then matching with
   register bit SUN4I_TCON0_IO_POL_DCLK_DRIVE_NEGEDGE
- correct commit log according to V4->V5 changes
V5->V6:
- fix typo in SUN4I_TCON0_IO_POL_DCLK_DRIVE_NEGEDGE as suggested by Marjan
---
  drivers/gpu/drm/sun4i/sun4i_tcon.c | 21 ++-------------------
  drivers/gpu/drm/sun4i/sun4i_tcon.h |  1 +
  2 files changed, 3 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
index eaaf5d70e352..6b9af4c08cd6 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
@@ -569,30 +569,13 @@ 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_DRIVE_NEGEDGE;
regmap_update_bits(tcon->regs, SUN4I_TCON0_IO_POL_REG,
  			   SUN4I_TCON0_IO_POL_HSYNC_POSITIVE |
  			   SUN4I_TCON0_IO_POL_VSYNC_POSITIVE |
+			   SUN4I_TCON0_IO_POL_DCLK_DRIVE_NEGEDGE |
  			   SUN4I_TCON0_IO_POL_DE_NEGATIVE,
  			   val);
diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.h b/drivers/gpu/drm/sun4i/sun4i_tcon.h
index cfbf4e6c1679..c5ac1b02482c 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_DRIVE_NEGEDGE		BIT(26)
  #define SUN4I_TCON0_IO_POL_HSYNC_POSITIVE		BIT(25)
  #define SUN4I_TCON0_IO_POL_VSYNC_POSITIVE		BIT(24)
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