---

yaml
---
r: 271222
b: refs/heads/master
c: d318954
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: def76608681983c1fe70c0fa780d8fe777442ef5
+refs/heads/master: d3189545ee69527e949769b89a4cbb331de97b4a

trunk/Documentation/fb/udlfb.txt

@@ -105,6 +105,11 @@ console		Allow fbcon to attach to udlfb provided framebuffers. This
 		the first framebuffer it finds, which isn't usually what the
 		user wants in the case of USB displays.
 
+shadow		Allocate a 2nd framebuffer to shadow what's currently across
+		the USB bus in device memory. If any pixels are unchanged,
+		do not transmit. Spends host memory to save USB transfers.
+		Enabled by default. Only disable on very low memory systems.
+
 Sysfs Attributes
 ================
 

trunk/drivers/video/udlfb.c

@@ -62,6 +62,7 @@ MODULE_DEVICE_TABLE(usb, id_table);
 /* module options */
 static int console;   /* Optionally allow fbcon to consume first framebuffer */
 static int fb_defio;  /* Optionally enable experimental fb_defio mmap support */
+static int shadow = 1; /* Optionally disable shadow framebuffer */
 
 /* dlfb keeps a list of urbs for efficient bulk transfers */
 static void dlfb_urb_completion(struct urb *urb);
@@ -1148,7 +1149,7 @@ static int dlfb_realloc_framebuffer(struct dlfb_data *dev, struct fb_info *info)
 	int new_len;
 	unsigned char *old_fb = info->screen_base;
 	unsigned char *new_fb;
-	unsigned char *new_back;
+	unsigned char *new_back = 0;
 
 	pr_warn("Reallocating framebuffer. Addresses will change!\n");
 
@@ -1180,7 +1181,8 @@ static int dlfb_realloc_framebuffer(struct dlfb_data *dev, struct fb_info *info)
 		 * But with imperfect damage info we may send pixels over USB
 		 * that were, in fact, unchanged - wasting limited USB bandwidth
 		 */
-		new_back = vzalloc(new_len);
+		if (shadow)
+			new_back = vzalloc(new_len);
 		if (!new_back)
 			pr_info("No shadow/backing buffer allocated\n");
 		else {
@@ -1593,6 +1595,7 @@ static int dlfb_usb_probe(struct usb_interface *interface,
 		usbdev->descriptor.bcdDevice, dev);
 	pr_info("console enable=%d\n", console);
 	pr_info("fb_defio enable=%d\n", fb_defio);
+	pr_info("shadow enable=%d\n", shadow);
 
 	dev->sku_pixel_limit = 2048 * 1152; /* default to maximum */
 
@@ -1950,6 +1953,9 @@ MODULE_PARM_DESC(console, "Allow fbcon to consume first framebuffer found");
 module_param(fb_defio, bool, S_IWUSR | S_IRUSR | S_IWGRP | S_IRGRP);
 MODULE_PARM_DESC(fb_defio, "Enable fb_defio mmap support. *Experimental*");
 
+module_param(shadow, bool, S_IWUSR | S_IRUSR | S_IWGRP | S_IRGRP);
+MODULE_PARM_DESC(shadow, "Shadow vid mem. Disable to save mem but lose perf");
+
 MODULE_AUTHOR("Roberto De Ioris <roberto@unbit.it>, "
 	      "Jaya Kumar <jayakumar.lkml@gmail.com>, "
 	      "Bernie Thompson <bernie@plugable.com>");