imx-drm: master bind failed: -517 with parallel_display (on i.MX6DL)

[Philipp Zabel]

On Tue, 2020-08-11 at 14:50 +0000, Stefan Birkholz wrote:
> Hello,
> 
> we are using the mainline kernel (currently on 4.19.128) successfully on an i.MX6DL-based system, but when we try to upgrade to any more recent kernel (>5.1) the display output stops working (screen is blank, backlight works). 
> 
> The relevant entries from the kernel log seem to be:
> [    8.954942] imx-drm display-subsystem: bound imx-ipuv3-crtc.3 (ops imx_drm_exit [imxdrm])
> [    9.028406] imx-drm display-subsystem: failed to bind disp0 (ops imx_pd_ops [parallel_display]): -517
> [    9.037873] imx-drm display-subsystem: master bind failed: -517

The only call in imx_pd_bind() I would expect to return -EPROBE_DEFER is
drm_of_find_panel_or_bridge(), maybe parallel-display node's port at 1 is
connected to a panel that is not registered. Are the drivers for the
panel and all its dependencies (power supply regulator, backlight)
enabled and probed?

regards
Philipp