drm_bridge_attach has stacked the bridge chain, so the bridge that gets pushed last can trigger its bridge function pre_enable first from drm_atomic_bridge_chain_pre_enable.
This indeed gives a chance to trigger slave bridge pre_enable first without triggering its host bridge pre_enable for the usual host to slave device model like DSI host with panel slave.
For fully enabled bridge drivers, host bridge pre_enable has all host related clock, reset, PHY configuration code that needs to initialized before sending commands or configuration from a slave to communicate its host.
Queue the bridge chain instead of stacking it so-that the bridges that got enqueued first can have a chance to trigger first.
Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Thomas Zimmermann tzimmermann@suse.de Signed-off-by: Jagan Teki jagan@amarulasolutions.com --- Changes for v3: - new patch
drivers/gpu/drm/drm_bridge.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c index 64f0effb52ac..e75d1a080c55 100644 --- a/drivers/gpu/drm/drm_bridge.c +++ b/drivers/gpu/drm/drm_bridge.c @@ -191,9 +191,9 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge, bridge->encoder = encoder;
if (previous) - list_add(&bridge->chain_node, &previous->chain_node); + list_add_tail(&bridge->chain_node, &previous->chain_node); else - list_add(&bridge->chain_node, &encoder->bridge_chain); + list_add_tail(&bridge->chain_node, &encoder->bridge_chain);
if (bridge->funcs->attach) { ret = bridge->funcs->attach(bridge, flags);