Hi Daniel,
Thanks for the tip. I just enabled fb.lockless_register_fb=1 and still cannot see any debug messages after the console_lock... :(
Regards, C.Palminha
On 22-01-2016 07:53, Daniel Vetter wrote:
Every new KMS driver writer seems to run into this and wonder how exactly drm_fb_helper_initial_config can die doing nothing at all. Set up some big warnings signs around this newbie trap to avoid future frustration and wasting everyone's time.
Cc: Carlos Palminha CARLOS.PALMINHA@synopsys.com Cc: Xinliang Liu xinliang.liu@linaro.org Cc: laurent.pinchart@ideasonboard.com Signed-off-by: Daniel Vetter daniel.vetter@intel.com
drivers/gpu/drm/drm_fb_helper.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+)
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c index 1e103c4c6ee0..9bf84b227613 100644 --- a/drivers/gpu/drm/drm_fb_helper.c +++ b/drivers/gpu/drm/drm_fb_helper.c @@ -2091,6 +2091,28 @@ out:
- drm_fb_helper_fill_fix() are provided as helpers to setup simple default
- values for the fbdev info structure.
- HANG DEBUGGING:
- When you have fbcon support built-in or already loaded, this function will do
- a full modeset to setup the fbdev console. And due to locking misdesign in
- the VT/fbdev subsystem that entire modeset sequence has to be done while
- holding console_lock. And until console_unlock is called no dmesg lines will
- be sent out to consoles, not even serial console. Which means when your
- driver crashes, you will see absolutely nothing else but a system stuck in
- this function, with no further output. And any kind of printk() you place
- within your own driver or in the drm core modeset code will also never show
- up.
- Standard debug practice is to run the fbcon setup without taking the
- console_lock as a hack, to be able to see backtraces and crashes on the
- serial line. This can be done by setting the fb.lockless_register_fb=1 kernel
- cmdline option.
- The other option is to just disable fbdev emulation since very likely the
- first modest from userspace will crash in the same way, and is even easier to
- debug. This can be done by setting the drm_kms_helper.fbdev_emulation=0
- kernel cmdline option.
*/
- RETURNS:
- Zero if everything went ok, nonzero otherwise.