udlfb: Add module_param to allow forcing pixel_limit

Some user scenarios need to prioritize performance over
maxiumum resolution.

Also, some devices may have bad vendor descriptors, and
this allows the user to set a pixel limit that matches
their specific device to avoid blank screens on higher
resolution monitors.

700000 minimum for DL-115, 2360000 maximum for DL-195

Signed-off-by: Ben Collins <bcollins@ubuntu.com>
Signed-off-by: Bernie Thompson <bernie@plugable.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/drivers/video/udlfb.c b/drivers/video/udlfb.c
index 4330cf4b17a3..86c8b256e306 100644
--- a/drivers/video/udlfb.c
+++ b/drivers/video/udlfb.c
@@ -72,6 +72,7 @@ MODULE_DEVICE_TABLE(usb, id_table);
 static bool console = 1; /* Allow fbcon to open framebuffer */
 static bool fb_defio = 1;  /* Detect mmap writes using page faults */
 static bool shadow = 1; /* Optionally disable shadow framebuffer */
+static int pixel_limit; /* Optionally force a pixel resolution limit */
 
 /* dlfb keeps a list of urbs for efficient bulk transfers */
 static void dlfb_urb_completion(struct urb *urb);
@@ -1616,6 +1617,14 @@ static int dlfb_usb_probe(struct usb_interface *interface,
                 goto error;
         }
 
+        if (pixel_limit) {
+                pr_warn("DL chip limit of %d overriden"
+                        " by module param to %d\n",
+                        dev->sku_pixel_limit, pixel_limit);
+                dev->sku_pixel_limit = pixel_limit;
+        }
+
+
         if (!dlfb_alloc_urb_list(dev, WRITES_IN_FLIGHT, MAX_TRANSFER)) {
                 retval = -ENOMEM;
                 pr_err("dlfb_alloc_urb_list failed\n");
@@ -1963,6 +1972,9 @@ MODULE_PARM_DESC(fb_defio, "Page fault detection of mmap writes");
 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_param(pixel_limit, int, S_IWUSR | S_IRUSR | S_IWGRP | S_IRGRP);
+MODULE_PARM_DESC(pixel_limit, "Force limit on max mode (in x*y pixels)");
+
 MODULE_AUTHOR("Roberto De Ioris <roberto@unbit.it>, "
               "Jaya Kumar <jayakumar.lkml@gmail.com>, "
               "Bernie Thompson <bernie@plugable.com>");