gpu: ipu-di: Add ipu_di_adjust_videomode()

On some monitors, high resolution modes are not working, exhibiting
pixel column truncation problems (for example, 1280x1024 displays as
1280x1022).

The function ipu_di_adjust_videomode() aims to fix these issues by
adjusting a passed videomode to IPU restrictions. The function can
be called from the drm_crtc_helper_funcs->mode_fixup() methods.

Signed-off-by: Jiada Wang <jiada_wang@mentor.com>
Signed-off-by: Deepak Das <deepak_das@mentor.com>
Signed-off-by: Steve Longerbeam <steve_longerbeam@mentor.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

drivers/gpu/ipu-v3/ipu-di.c

@@ -511,6 +511,35 @@ static void ipu_di_config_clock(struct ipu_di *di,
 		clk_get_rate(di->clk_di_pixel) / (clkgen0 >> 4));
 }
 
+/*
+ * This function is called to adjust a video mode to IPU restrictions.
+ * It is meant to be called from drm crtc mode_fixup() methods.
+ */
+int ipu_di_adjust_videomode(struct ipu_di *di, struct videomode *mode)
+{
+	u32 diff;
+
+	if (mode->vfront_porch >= 2)
+		return 0;
+
+	diff = 2 - mode->vfront_porch;
+
+	if (mode->vback_porch >= diff) {
+		mode->vfront_porch = 2;
+		mode->vback_porch -= diff;
+	} else if (mode->vsync_len > diff) {
+		mode->vfront_porch = 2;
+		mode->vsync_len = mode->vsync_len - diff;
+	} else {
+		dev_warn(di->ipu->dev, "failed to adjust videomode\n");
+		return -EINVAL;
+	}
+
+	dev_warn(di->ipu->dev, "videomode adapted for IPU restrictions\n");
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ipu_di_adjust_videomode);
+
 int ipu_di_init_sync_panel(struct ipu_di *di, struct ipu_di_signal_cfg *sig)
 {
 	u32 reg;

include/video/imx-ipu-v3.h

@@ -17,6 +17,7 @@
 #include <linux/bitmap.h>
 #include <linux/fb.h>
 #include <media/v4l2-mediabus.h>
+#include <video/videomode.h>
 
 struct ipu_soc;
 
@@ -236,6 +237,7 @@ void ipu_di_put(struct ipu_di *);
 int ipu_di_disable(struct ipu_di *);
 int ipu_di_enable(struct ipu_di *);
 int ipu_di_get_num(struct ipu_di *);
+int ipu_di_adjust_videomode(struct ipu_di *di, struct videomode *mode);
 int ipu_di_init_sync_panel(struct ipu_di *, struct ipu_di_signal_cfg *sig);
 
 /*