[This is a third submission of a message that vger first bounched from
my Yahoo account, and then
from gmail when I failed to disable HTML formatting. I apologize if
it is a duplicate or triplicate. -Adam]
Hello, Bernie.
In Linux-4.0-rc3, the DisplayLink driver gets a kernel memory fault when its
USB device is unplugged, specifically when vblank_disable_and_save in
linux-4.0-rc3/drivers/gpu/drm/drm_irq.c attempts to call the NULL function
pointer dev->driver_get_vblank_counter.
linux-4.0-rc3/Documentation/DocBook/drm.tmpl says of that field, "Otherwise
drivers can use the drm_vblank_count helper function to handle this
operation." Trying that seems to have eliminated the oops when I unplug the
device, although I do see these lines in the console log at device driver
initialization time that I think are probably fine, but which I should
mention in case the indicate that I did the wrong the thing:
[drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[drm] No driver support for vblank timestamp query.
If that doesn't look like a problem to you, then I suggest you apply the
patch, appended below and also included as an attachment, and push the
change upstream. The patch just adds one line that appears in six other
framebuffer drivers to initialize the driver_get_vblank_counter drm_driver
function.
Thank you for maintaining the USB DisplayLink driver, and thanks for your
attention to this.
Adam Richter
--- drivers/gpu/drm/udl/udl_drv.c.orig 2015-03-09 22:10:14.292335527 -0700
+++ drivers/gpu/drm/udl/udl_drv.c 2015-03-09 22:22:14.148342842 -0700
@@ -41,6 +41,7 @@ static struct drm_driver driver = {
.load = udl_driver_load,
.unload = udl_driver_unload,
.set_busid = udl_driver_set_busid,
+ .get_vblank_counter = drm_vblank_count,
/* gem hooks */
.gem_free_object = udl_gem_free_object,
--- drivers/gpu/drm/udl/udl_drv.c.orig 2015-03-09 22:10:14.292335527 -0700
+++ drivers/gpu/drm/udl/udl_drv.c 2015-03-09 22:22:14.148342842 -0700
@@ -41,6 +41,7 @@ static struct drm_driver driver = {
.load = udl_driver_load,
.unload = udl_driver_unload,
.set_busid = udl_driver_set_busid,
+ .get_vblank_counter = drm_vblank_count,
/* gem hooks */
.gem_free_object = udl_gem_free_object,
