video: speedup writing strings to fb console

With enabled framebuffer console the printenv command can take several
seconds to complete. This patch temporarily disables cache flush when
writing strings to fb console. Then there is no noticable delay anymore.

Tested with imx6 hdmi framebuffer.

Signed-off-by: Soeren Moch <smoch@web.de>
Acked-by: Stefano Babic <sbabic@denx.de>

drivers/video/cfb_console.c

@@ -1160,10 +1160,19 @@ static void video_putc(struct stdio_dev *dev, const char c)
 
 static void video_puts(struct stdio_dev *dev, const char *s)
 {
+	int flush = cfb_do_flush_cache;
 	int count = strlen(s);
 
+	/* temporarily disable cache flush */
+	cfb_do_flush_cache = 0;
+
 	while (count--)
 		video_putc(dev, *s++);
+
+	if (flush) {
+		cfb_do_flush_cache = flush;
+		flush_cache(VIDEO_FB_ADRS, VIDEO_SIZE);
+	}
 }
 
 /*