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Commit d3189545ee69527e949769b89a4cbb331de97b4a

Authored by Stuart Hopkins
Committed by Florian Tobias Schandinat
1 parent def7660868
Exists in master and in 6 other branches imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga, smarc-l5.0.0_1.0.0-ga

udlfb: Add module option to do without shadow framebuffer 

By default, udlfb allocates a 2nd buffer to shadow what's across
the bus on the USB device.  It can operate without this shadow,
but then it cannot tell which pixels have changed, and must send all.

Saves host memory, but worsens the USB 2.0 bus bottleneck.

This option allows users in very low memory situations (e.g.
bifferboard) to optionally turn off this shadow framebuffer.

Signed-off-by: Stuart Hopkins <stuart@linux-depot.com>
Signed-off-by: Bernie Thompson <bernie@plugable.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>

Showing 2 changed files with 13 additions and 2 deletions Side-by-side Diff

Documentation/fb/udlfb.txt
Diff comments   View file @ d318954
... ... @@ -105,6 +105,11 @@
105 105 the first framebuffer it finds, which isn't usually what the
106 106 user wants in the case of USB displays.
107 107  
  108 +shadow Allocate a 2nd framebuffer to shadow what's currently across
  109 + the USB bus in device memory. If any pixels are unchanged,
  110 + do not transmit. Spends host memory to save USB transfers.
  111 + Enabled by default. Only disable on very low memory systems.
  112 +
108 113 Sysfs Attributes
109 114 ================
110 115  
drivers/video/udlfb.c
Diff comments   View file @ d318954
... ... @@ -62,6 +62,7 @@
62 62 /* module options */
63 63 static int console; /* Optionally allow fbcon to consume first framebuffer */
64 64 static int fb_defio; /* Optionally enable experimental fb_defio mmap support */
  65 +static int shadow = 1; /* Optionally disable shadow framebuffer */
65 66  
66 67 /* dlfb keeps a list of urbs for efficient bulk transfers */
67 68 static void dlfb_urb_completion(struct urb *urb);
... ... @@ -1148,7 +1149,7 @@
1148 1149 int new_len;
1149 1150 unsigned char *old_fb = info->screen_base;
1150 1151 unsigned char *new_fb;
1151   - unsigned char *new_back;
  1152 + unsigned char *new_back = 0;
1152 1153  
1153 1154 pr_warn("Reallocating framebuffer. Addresses will change!\n");
1154 1155  
... ... @@ -1180,7 +1181,8 @@
1180 1181 * But with imperfect damage info we may send pixels over USB
1181 1182 * that were, in fact, unchanged - wasting limited USB bandwidth
1182 1183 */
1183   - new_back = vzalloc(new_len);
  1184 + if (shadow)
  1185 + new_back = vzalloc(new_len);
1184 1186 if (!new_back)
1185 1187 pr_info("No shadow/backing buffer allocated\n");
1186 1188 else {
... ... @@ -1593,6 +1595,7 @@
1593 1595 usbdev->descriptor.bcdDevice, dev);
1594 1596 pr_info("console enable=%d\n", console);
1595 1597 pr_info("fb_defio enable=%d\n", fb_defio);
  1598 + pr_info("shadow enable=%d\n", shadow);
1596 1599  
1597 1600 dev->sku_pixel_limit = 2048 * 1152; /* default to maximum */
1598 1601  
... ... @@ -1949,6 +1952,9 @@
1949 1952  
1950 1953 module_param(fb_defio, bool, S_IWUSR | S_IRUSR | S_IWGRP | S_IRGRP);
1951 1954 MODULE_PARM_DESC(fb_defio, "Enable fb_defio mmap support. *Experimental*");
  1955 +
  1956 +module_param(shadow, bool, S_IWUSR | S_IRUSR | S_IWGRP | S_IRGRP);
  1957 +MODULE_PARM_DESC(shadow, "Shadow vid mem. Disable to save mem but lose perf");
1952 1958  
1953 1959 MODULE_AUTHOR("Roberto De Ioris <roberto@unbit.it>, "
1954 1960 "Jaya Kumar <jayakumar.lkml@gmail.com>, "