i915: eDP hot-unplug errors

[Linus Torvalds]

Oops. This got sent without the right Cc, and the wrong subject (the
people who were *supposed* to be cc'd instead got into the subject
line, and the subject line got dropped entirely).

                    Linus

On Sun, May 27, 2012 at 4:09 PM, Linus Torvalds
<torvalds at linux-foundation.org> wrote:
> A new worry about excessively verbose i915 driver "errors" that don't
> actually seem to be errors.
>
> I got myself a micro-DP to VGA adapter so that I can use my Macbook
> Air for presentations.
>
> And testing it, hotplugging seems to work very nicely, and gone are
> the days when you had to do xrandr and crap. Things "JustWork(tm)".
>
> Goodie.
>
> Until you start looking at the dmesg log. Then it gets ugly. It's full
> of scary-looking stuff like
>
>  ------------[ cut here ]------------
>  WARNING: at drivers/gpu/drm/i915/intel_dp.c:350 intel_dp_check_edp+0x5d/0xb0()
>  Hardware name: MacBookAir4,1
>  eDP powered off while attempting aux channel communication.
>  Modules linked in: fuse rfcomm bnep nf_conntrack_netbios_ns
> nf_conntrack_broadcast ..
>  Pid: 2126, comm: kworker/0:0 Tainted: G        W    3.4.0-08209-gae32adc #9
>  Call Trace:
>    warn_slowpath_common+0x7a/0xb0
>    warn_slowpath_fmt+0x41/0x50
>    intel_dp_check_edp+0x5d/0xb0
>    intel_dp_aux_ch+0x3f/0x330
>    intel_dp_aux_native_read_retry+0xad/0x130
>    intel_dp_detect+0x240/0x2c0
>    output_poll_execute+0xba/0x1a0
>    process_one_work+0x11b/0x3c0
>    worker_thread+0x12e/0x2d0
>    kthread+0x8e/0xa0
>    kernel_thread_helper+0x4/0x10
>  ---[ end trace 5756a4d08d9e2a83 ]---
>
> which seems a bit extreme. I just unplugged the connector, I don't
> think it should necessarily make quite this big a deal over it. What
> does the WARN_ON() with the full call trace really buy us?
>
>                   Linus