[PATCH 2/3] drm: lcdif: Use dedicated set/clr registers for polarity/edge

Paul Kocialkowski
2026-03-30T22:48:42Z

The lcdif v3 hardware comes with dedicated registers to set and clear
polarity bits in the CTRL register. It is unclear if there is a
difference with writing to the CTRL register directly.

Follow the NXP BSP reference by using these registers, in case there is
a subtle difference caused by using them.

Signed-off-by: Paul Kocialkowski <paulk@sys-base.io>
---
drivers/gpu/drm/mxsfb/lcdif_kms.c | 23 ++++++++++++++++-------
1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/mxsfb/lcdif_kms.c b/drivers/gpu/drm/mxsfb/lcdif_kms.c
index a00c4f6d63f4..1aac354041c7 100644
--- a/drivers/gpu/drm/mxsfb/lcdif_kms.c
+++ b/drivers/gpu/drm/mxsfb/lcdif_kms.c
@@ -296,18 +296,27 @@ static void lcdif_set_formats(struct lcdif_drm_private *lcdif,
static void lcdif_set_mode(struct lcdif_drm_private *lcdif, u32 bus_flags)
{
struct drm_display_mode *m = &lcdif->crtc.state->adjusted_mode;
- u32 ctrl = 0;
+ u32 ctrl;

if (m->flags & DRM_MODE_FLAG_NHSYNC)
- ctrl |= CTRL_INV_HS;
+ writel(CTRL_INV_HS, lcdif->base + LCDC_V8_CTRL + REG_SET);
+ else
+ writel(CTRL_INV_HS, lcdif->base + LCDC_V8_CTRL + REG_CLR);
+
if (m->flags & DRM_MODE_FLAG_NVSYNC)
- ctrl |= CTRL_INV_VS;
+ writel(CTRL_INV_VS, lcdif->base + LCDC_V8_CTRL + REG_SET);
+ else
+ writel(CTRL_INV_VS, lcdif->base + LCDC_V8_CTRL + REG_CLR);
+
if (bus_flags & DRM_BUS_FLAG_DE_LOW)
- ctrl |= CTRL_INV_DE;
- if (bus_flags & DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE)
- ctrl |= CTRL_INV_PXCK;
+ writel(CTRL_INV_DE, lcdif->base + LCDC_V8_CTRL + REG_SET);
+ else
+ writel(CTRL_INV_DE, lcdif->base + LCDC_V8_CTRL + REG_CLR);

- writel(ctrl, lcdif->base + LCDC_V8_CTRL);
+ if (bus_flags & DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE)
+ writel(CTRL_INV_PXCK, lcdif->base + LCDC_V8_CTRL + REG_SET);
+ else
+ writel(CTRL_INV_PXCK, lcdif->base + LCDC_V8_CTRL + REG_CLR);

writel(DISP_SIZE_DELTA_Y(m->vdisplay) |
DISP_SIZE_DELTA_X(m->hdisplay),
--
2.53.0