[PATCH 10/13] drm/fb-helper: Support deferred setup

[Maarten Lankhorst]

Op 04-07-17 om 17:18 schreef Daniel Vetter:
> FB helper code falls back to a 1024x768 mode if no outputs are connected
> or don't report back any modes upon initialization. This can be annoying
> because outputs that are added to FB helper later on can't be used with
> FB helper if they don't support a matching mode.
>
> The fallback is in place because VGA connectors can happen to report an
> unknown connection status even when they are in fact connected.
>
> Some drivers have custom solutions in place to defer FB helper setup
> until at least one output is connected. But the logic behind these
> solutions is always the same and there is nothing driver-specific about
> it, so a better alterative is to fix the FB helper core and add support
> for all drivers automatically.
>
> This patch adds support for deferred FB helper setup. It checks all the
> connectors for their connection status, and if all of them report to be
> disconnected marks the FB helper as needing deferred setup. Whet setup
> is deferred, the FB helper core will automatically retry setup after a
> hotplug event, and it will keep trying until it succeeds.
>
> v2: Rebase onto my entirely reworked fbdev helper locking. One big
> difference is that this version again drops&reacquires the fbdev lock
> (which is now fb_helper->lock, but before this patch series it was
> mode_config->mutex), because register_framebuffer must be able to
> recurse back into fbdev helper code for the initial screen setup.
>
> v3: __drm_fb_helper_initial_config must hold fb_helper->lock upon
> return, I've fumbled that in the deferred setup case (Liviu).
>
> v4: I was blind, redo this all. __drm_fb_helper_initial_config
> shouldn't need to reacquire fb_helper->lock, that just confuses
> callers. I myself got confused by kernel_fb_helper_lock and somehow
> thought it's the same as fb_helper->lock. Tsk.
>
> Also simplify the logic a bit (we don't need two functions to probe
> connectors), we can stick much closer to the existing code. And update
> some comments I've spotted that are outdated.
>
> v5: Don't pass -EAGAIN to drivers, it's just an internal error code
> (Liviu).
>
> v6: Add _and_unlock suffix to clarify locking (Maarten)
If you remove intel_fbdev_output_poll_changed's null check for ifbdev->fb,
and apply 11 before this one, then for the first 11 patches:

Reviewed-by: Maarten Lankhorst <maarten.lankhorst at intel.com>

It should probably be noted in this commit that this change results in no longer registering the intel fb if no output is connected,
in which case dummy fb is always used.