Hi Daniel, Thank you for the patch. On Friday 22 January 2016 08:53:45 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@xxxxxxxxxxxx> > Cc: Xinliang Liu <xinliang.liu@xxxxxxxxxx> > Cc: laurent.pinchart@xxxxxxxxxxxxxxxx > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> > --- > 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 No need to start the sentence with "And", s/And due/Due/ will do. > 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 Same here. > will > + * be sent out to consoles, not even serial console. Which means when your Similarly, s/Which means when/This means that if/ > + * 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 s/And any/Any/ Apart from that, Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> Very useful addition to the documentation, I got bitten by this more than once. I wonder whether we could make this information even easier to find. > 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. > */ -- Regards, Laurent Pinchart _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
