[Intel-gfx] [PATCH] drm/atomic: Acquire connection_mutex lock in drm_helper_probe_single_connector_modes.

[Boris Brezillon]

On Wed, 29 Mar 2017 15:26:45 +0200
Daniel Vetter <daniel at ffwll.ch> wrote:

> On Wed, Mar 29, 2017 at 12:16:50PM +0200, Maarten Lankhorst wrote:
> > mode_valid() and get_modes() called
> > from drm_helper_probe_single_connector_modes()
> > may need to look at connector->state because what a valid mode is may
> > depend on connector properties being set. For example some HDMI modes
> > might be rejected when a connector property forces the connector
> > into DVI mode.
> > 
> > Some implementations of detect() already lock all state,
> > so we have to pass an acquire_ctx to them to prevent a deadlock.
> > 
> > This means changing the function signature of detect() slightly,
> > and passing the acquire_ctx for locking multiple crtc's.
> > It might be NULL, in which case expensive operations should be avoided.
> > 
> > intel_dp.c however ignores the force flag, so still lock
> > connection_mutex there if needed.
> > 
> > Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> > Cc: Boris Brezillon <boris.brezillon at free-electrons.com>
> > Cc: Manasi Navare <manasi.d.navare at intel.com>  
> 
> Hm only noticed this now, but mixing up force with the acquire_ctx sounds
> like very bad interface design. Yes, the only user of the new hook works
> like that, but that's really accidental I think. I think just having the
> ctx everywhere (for atomic drivers at least) would be a lot safer. This is
> extremely surprising (and undocumented suprise at that).

Yes, I was about to say the same thing: the interface is not very
clear, and I don't understand why ctx = NULL implies force = false.