[PATCH] drm/exynos/dsi: simplify hotplug code

[Thierry Reding]

On Thu, Nov 06, 2014 at 12:35:48PM +0100, Andrzej Hajda wrote:
> Exynos DSI driver uses DSI bus attach/detach callbacks to implement
> panel hotplug mechanism. The patch moves panel attachment code
> from .detect callback to DSI bus callbacks. It makes the code
> simpler and more straightforward.
> The patch removes also redundant and lock unprotected dpms_off call
> from unbind code.
> 
> Signed-off-by: Andrzej Hajda <a.hajda at samsung.com>
> ---
> Hi,
> 
> This patch simplifies drm part of hotplug mechanism in dsi attach/detach callbacks.
> It also fixes minor bug with unprotected dpms_off call, which is unneccesary anyway.
> 
> But the main reason I have looked at this code again is to show that
> we do not need zombie panels, we can kill panels properly if we have hot plug/unplug
> callbacks. And it is quite simple: we just need to take mode_config.mutex locks
> to synchronize dsi callbacks with drm, nothing more.
> It works nicely because of two things:
> - panel callbacks are called always under this lock,
> - callbacks are installed after drmdev creation and deinstalled before drmdev destroy - 
> this way we assure drmdev is always present in callbacks.

Again, something like what you propose is going to work only for DSI
devices. What we need is a solution that works for all other types of
panels, too. This is even more important when we consider bridges
because they are less likely to be on a DSI bus.

Thierry
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