[Intel-gfx] [PATCH 01/13] drm/fb-helper: Push down modeset lock into FB helpers

[Maarten Lankhorst]

Op 29-06-17 om 11:23 schreef Daniel Vetter:
> On Thu, Jun 29, 2017 at 11:10 AM, Maarten Lankhorst
> <maarten.lankhorst at linux.intel.com> wrote:
>> Op 27-06-17 om 16:59 schreef Daniel Vetter:
>>> From: Thierry Reding <treding at nvidia.com>
>>>
>>> Move the modeset locking from drivers into FB helpers.
>>>
>>> v2: Also handle intel_connector_add_to_fbdev.
>>>
>>> Tested-by: John Stultz <john.stultz at linaro.org>
>>> Signed-off-by: Thierry Reding <treding at nvidia.com> (v1)
>>> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
>>> ---
>>>  drivers/gpu/drm/drm_fb_helper.c        | 40 +++++++++++++++++++++++++++++-----
>>>  drivers/gpu/drm/i915/intel_dp_mst.c    |  6 -----
>>>  drivers/gpu/drm/radeon/radeon_dp_mst.c |  7 ------
>>>  3 files changed, 34 insertions(+), 19 deletions(-)
>> I know we suck at DP-MST. But I fear the unregister leaves open a race with mst_port being unset without connection_mutex..
>>
>> best_encoder() and mode_valid() appear to use it. It's probably harmless and I have no good solution, so maybe just annotate it in the patch? Might also affect i915_hpd_poll_init_work, though I think the race in itself is harmless.
> Hm, but this did race even before that already ... Should I just wrap
> the mst_port = NULL in the connection_mutex? With a big warning that
> we should have proper refcounting for this instead (both connectors
> and all the mst things are refcounted already).
> -Daniel

I think leave open the race, the DP-MST modeset code itself doesn't use the connector->mst_port, just the detect callbacks do. In case of nonblocking modeset mst_port might already fall away so it's not like the race is any worse now.

I don't even know how to solve it, except by not unplugging. :)

~Maarten