[PATCH 4/5] drm: Push drm_global_mutex locking in drm_open

[Chris Wilson]

Quoting Daniel Vetter (2020-02-04 15:01:45)
> We want to only take the BKL on crap drivers, but to know whether
> we have a crap driver we first need to look it up. Split this shuffle
> out from the main BKL-disabling patch, for more clarity. Historical
> aside: When the kernel-wide BKL was removed, it was replaced by
> drm_global_mutex within the scope of the drm subsystem hence why these
> two things are (almost) interchangeable as concepts here.
> 
> Since the minors are refcounted drm_minor_acquire is purely internal
> and this does not have a driver visible effect.
> 
> v2: Push the locking even further into drm_open(), suggested by Chris.
> This gives us more symmetry with drm_release(), and maybe a futuer
> avenue where we make drm_global_mutex locking (partially) opt-in like
> with drm_release_noglobal().
> 
> v3:
> - Actually push this stuff correctly, don't unlock twice (Chris)
> - Fix typo on commit message, plus explain why BKL = drm_global_mutex
>   (Sam)
> 
> Cc: Sam Ravnborg <sam at ravnborg.org>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris