drm/tegra: dc: Restore coupling of display controllers

BugLink: https://bugs.launchpad.net/bugs/1923069
commit a31500fe7055451ed9043c8fff938dfa6f70ee37 upstream.

Coupling of display controllers used to rely on runtime PM to take the
companion controller out of reset. Commit fd67e9c6ed5a ("drm/tegra: Do
not implement runtime PM") accidentally broke this when runtime PM was
removed.

Restore this functionality by reusing the hierarchical host1x client
suspend/resume infrastructure that's similar to runtime PM and which
perfectly fits this use-case.

Fixes: fd67e9c6ed5a ("drm/tegra: Do not implement runtime PM")
Reported-by: Dmitry Osipenko <digetx@gmail.com>
Reported-by: Paul Fertser <fercerpav@gmail.com>
Tested-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>

diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
index 0ae3a025efe9d6f9566ef69a05021c627c16583a..8eeef5017826e5acc406b5fc0cde3b1cdacbd5c1 100644 (file)
--- a/drivers/gpu/drm/tegra/dc.c
+++ b/drivers/gpu/drm/tegra/dc.c
@@ -2501,22 +2501,18 @@ static int tegra_dc_couple(struct tegra_dc *dc)
         * POWER_CONTROL registers during CRTC enabling.
         */
        if (dc->soc->coupled_pm && dc->pipe == 1) {
-               u32 flags = DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_CONSUMER;
-               struct device_link *link;
-               struct device *partner;
+               struct device *companion;
+               struct tegra_dc *parent;
 
-               partner = driver_find_device(dc->dev->driver, NULL, NULL,
-                                            tegra_dc_match_by_pipe);
-               if (!partner)
+               companion = driver_find_device(dc->dev->driver, NULL, (const void *)0,
+                                              tegra_dc_match_by_pipe);
+               if (!companion)
                        return -EPROBE_DEFER;
 
-               link = device_link_add(dc->dev, partner, flags);
-               if (!link) {
-                       dev_err(dc->dev, "failed to link controllers\n");
-                       return -EINVAL;
-               }
+               parent = dev_get_drvdata(companion);
+               dc->client.parent = &parent->client;
 
-               dev_dbg(dc->dev, "coupled to %s\n", dev_name(partner));
+               dev_dbg(dc->dev, "coupled to %s\n", dev_name(companion));
        }
 
        return 0;