fbdev: mxsfb: implement FB_PRE_INIT_FB option

The FB_PRE_INIT_FB option keeps the kernel from reinitializing the display
and prevents flickering during the transition from a bootloader splash
screen to the kernel logo screen.

Make this option available for the mxsfb driver.
Signed-off-by: Melchior Franz <melchior.franz@ginzinger.com>
Signed-off-by: Martin Kepplinger <martin.kepplinger@ginzinger.com>
Signed-off-by: Manfred Schlaegl <manfred.schlaegl@ginzinger.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
Cc: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>

drivers/video/fbdev/Kconfig

@@ -2183,7 +2183,7 @@ config FB_EP93XX
 
 config FB_PRE_INIT_FB
 	bool "Don't reinitialize, use bootloader's GDC/Display configuration"
-	depends on FB && FB_MB862XX_LIME
+	depends on FB && (FB_MB862XX_LIME || FB_MXS)
 	---help---
 	  Select this option if display contents should be inherited as set by
 	  the bootloader.

drivers/video/fbdev/mxsfb.c

@@ -181,6 +181,7 @@ struct mxsfb_info {
 	const struct mxsfb_devdata *devdata;
 	u32 sync;
 	struct regulator *reg_lcd;
+	int pre_init;
 };
 
 #define mxsfb_is_v3(host) (host->devdata->ipversion == 3)
@@ -419,6 +420,12 @@ static int mxsfb_set_par(struct fb_info *fb_info)
 
 	fb_info->fix.line_length = line_size;
 
+	if (host->pre_init) {
+		mxsfb_enable_controller(fb_info);
+		host->pre_init = 0;
+		return 0;
+	}
+
 	/*
 	 * It seems, you can't re-program the controller if it is still running.
 	 * This may lead into shifted pictures (FIFO issue?).
@@ -931,6 +938,10 @@ static int mxsfb_probe(struct platform_device *pdev)
 	if (IS_ERR(host->reg_lcd))
 		host->reg_lcd = NULL;
 
+#if defined(CONFIG_FB_PRE_INIT_FB)
+	host->pre_init = 1;
+#endif
+
 	fb_info->pseudo_palette = devm_kcalloc(&pdev->dev, 16, sizeof(u32),
 					       GFP_KERNEL);
 	if (!fb_info->pseudo_palette) {
@@ -963,6 +974,7 @@ static int mxsfb_probe(struct platform_device *pdev)
 		mxsfb_enable_controller(fb_info);
 	}
 
+	host->pre_init = 0;
 	dev_info(&pdev->dev, "initialized\n");
 
 	return 0;