[PATCH v3 0/4] drm/panel: Handle the "panel is missing" case properly

[Thierry Reding]

On Wed, May 09, 2018 at 03:00:38PM +0200, Boris Brezillon wrote:
> Hello,
> 
> This is a new attempt at fixing the "panel is missing" issue (described
> in this thread [1]). I lost track of Eric's proposal, but I recently
> proposed to address this problem through a new ->detect() hook in the
> panel_funcs interface [2], which was rejected.
> 
> So here is a new version based on the feedback I had from Daniel,
> Thierry and Rob.
> 
> The idea is to allow of_drm_find_panel() to return -ENODEV and let the
> DRM driver decide what to do with that (silently ignore the missing
> component and register the DRM device, or fail to register the DRM
> device).
> 
> Patch 1 changes the semantic of of_drm_find_panel() so that it returns
> an ERR_PTR() instead of NULL when the panel is not found. This way
> we'll be able to differentiate the "panel is missing" from "panel has
> not been probed yet" errors.
> 
> Patch 2 and 3 are adding new tests in of_drm_find_panel() and
> drm_of_find_panel_or_bridge() to return -ENODEV when the status
> property of the DT node is not set to "okay".
> 
> Patch 4 is patching the VC4 DSI encoder driver to gracefully handle the
> -ENODEV case and allow the registration of the DRM device when the DSI
> device is disabled.
> 
> Note that patch 6 which was modifying the panel status prop from the
> I2C driver has been dropped because I'm not sure yet how to solve the
> "force probe of deferred-probe devices even if no new devices have been
> bound to drivers" problem. Anyway, even without this patch, the series
> still makes sense to handle the case where devices are described in the
> DT but marked "disabled" (either at compilation time or tweaked by the
> bootloader).
> 
> Regards,
> 
> Boris
> 
> Changes in v3:
> - Dropped patch 1 since it's been acked by Thierry and should be
>   applied soon (either through the drm-tegra or drm-misc tree)
> - Dropped patch 6 because we are still discussing who should mark
>   the device "disabled" or "fail" and how we should trigger the
>   re-probe of deferred-probe devices in this case
> 
> Changes in v2:
> - Everything :-)
> 
> [1]https://lists.freedesktop.org/archives/dri-devel/2017-November/157688.html
> [2]https://www.spinics.net/lists/dri-devel/msg174808.html

I don't exactly remember what we decided should be the merge path for
this, but I suspect someone else was supposed to pick it up because I
ended up acking these patches. However, since this hasn't been applied
yet, I decided to go ahead and apply this to drm-misc-next.

Thierry
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