drm/bridge: parade-ps8640: Handle DP AUX more properly
While it works, for the most part, to assume that the panel has finished probing when devm_of_dp_aux_populate_ep_devices() returns, it's a bit fragile. This is talked about at length in commit a1e3667a ("drm/bridge: ti-sn65dsi86: Promote the AUX channel to its own sub-dev"). When reviewing the ps8640 code, I managed to convince myself that it was OK not to worry about it there and that maybe it wasn't really _that_ fragile. However, it turns out that it really is. Simply hardcoding panel_edp_probe() to return -EPROBE_DEFER was enough to put the boot process into an infinite loop. I believe this manages to trip the same issues that we used to trip with the main MSM code where something about our actions trigger Linux to re-probe previously deferred devices right away and each time we try again we re-trigger Linux to re-probe. Let's fix this using the callback introduced in the patch ("drm/dp: Callbacks to make it easier for drivers to use DP AUX bus properly"). When using the new callback, we have to be a little careful. The probe_done() callback is no longer always called in the context of our probe routine. That means we can't rely on being able to return -EPROBE_DEFER from it. We re-jigger the order of things a bit to account for that. With this change, the device still boots (though obviously the panel doesn't come up) if I force panel-edp to always return -EPROBE_DEFER. If I fake it and make the panel probe exactly once it also works. Signed-off-by: Douglas Anderson <dianders@chromium.org> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org> Link: https://patchwork.freedesktop.org/patch/msgid/20220510122726.v3.4.Ia6324ebc848cd40b4dbd3ad3289a7ffb5c197779@changeid
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