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 <[email protected]>
---
 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

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