video: mxsfb: Fix framebuffer corruption on mx6sx

Allocate the framebuffer memory as coherent, otherwise the framebuffer
will suffer from artifacts when displaying scrolling text or video.
This can be replicated on i.MX6SX (armv7), which has more complex memory
architecture compared to the i.MX23/28 (armv5).
Signed-off-by: NMarek Vasut <marex@denx.de>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

drivers/video/fbdev/mxsfb.c

@@ -800,6 +800,7 @@ static int mxsfb_init_fbinfo(struct mxsfb_info *host,
 			struct fb_videomode *vmode)
 {
 	int ret;
+	struct device *dev = &host->pdev->dev;
 	struct fb_info *fb_info = &host->fb_info;
 	struct fb_var_screeninfo *var = &fb_info->var;
 	dma_addr_t fb_phys;
@@ -825,12 +826,10 @@ static int mxsfb_init_fbinfo(struct mxsfb_info *host,
 
 	/* Memory allocation for framebuffer */
 	fb_size = SZ_2M;
-	fb_virt = alloc_pages_exact(fb_size, GFP_DMA);
+	fb_virt = dma_alloc_wc(dev, PAGE_ALIGN(fb_size), &fb_phys, GFP_KERNEL);
 	if (!fb_virt)
 		return -ENOMEM;
 
-	fb_phys = virt_to_phys(fb_virt);
-
 	fb_info->fix.smem_start = fb_phys;
 	fb_info->screen_base = fb_virt;
 	fb_info->screen_size = fb_info->fix.smem_len = fb_size;
@@ -843,9 +842,11 @@ static int mxsfb_init_fbinfo(struct mxsfb_info *host,
 
 static void mxsfb_free_videomem(struct mxsfb_info *host)
 {
+	struct device *dev = &host->pdev->dev;
 	struct fb_info *fb_info = &host->fb_info;
 
-	free_pages_exact(fb_info->screen_base, fb_info->fix.smem_len);
+	dma_free_wc(dev, fb_info->screen_size, fb_info->screen_base,
+		    fb_info->fix.smem_start);
 }
 
 static const struct platform_device_id mxsfb_devtype[] = {