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Subject[PATCH v2] drm/mxsfb: fix pixel clock polarity
Date
The DRM subsystem specifies the pixel clock polarity from a
controllers perspective: DRM_BUS_FLAG_PIXDATA_NEGEDGE means
the controller drives the data on pixel clocks falling edge.
That is the controllers DOTCLK_POL=0 (Default is data launched
at negative edge).

Also change the data enable logic to be high active by default
and only change if explicitly requested via bus_flags. With
that defaults are:
- Data enable: high active
- Pixel clock polarity: controller drives data on negative edge

Signed-off-by: Stefan Agner <stefan@agner.ch>
---
Changes since v1:
- Improved comments/fixed typo

drivers/gpu/drm/mxsfb/mxsfb_crtc.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/mxsfb/mxsfb_crtc.c b/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
index 3770dd2..5556e53 100644
--- a/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
+++ b/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
@@ -195,9 +195,16 @@ static void mxsfb_crtc_mode_set_nofb(struct mxsfb_drm_private *mxsfb)
vdctrl0 |= VDCTRL0_HSYNC_ACT_HIGH;
if (m->flags & DRM_MODE_FLAG_PVSYNC)
vdctrl0 |= VDCTRL0_VSYNC_ACT_HIGH;
- if (bus_flags & DRM_BUS_FLAG_DE_HIGH)
+ /* Make sure Data Enable is high active by default */
+ if (!(bus_flags & DRM_BUS_FLAG_DE_LOW))
vdctrl0 |= VDCTRL0_ENABLE_ACT_HIGH;
- if (bus_flags & DRM_BUS_FLAG_PIXDATA_NEGEDGE)
+ /*
+ * DRM_BUS_FLAG_PIXDATA_ defines are controller centric,
+ * controllers VDCTRL0_DOTCLK is display centric.
+ * Drive on positive edge -> display samples on falling edge
+ * DRM_BUS_FLAG_PIXDATA_POSEDGE -> VDCTRL0_DOTCLK_ACT_FALLING
+ */
+ if (bus_flags & DRM_BUS_FLAG_PIXDATA_POSEDGE)
vdctrl0 |= VDCTRL0_DOTCLK_ACT_FALLING;

writel(vdctrl0, mxsfb->base + LCDC_VDCTRL0);
--
2.10.2
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