linux-kernel - [PATCH v3 5/7] drm: bridge: Queue the bridge chain instead of stacking

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Date:   Mon, 15 Feb 2021 01:11:00 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     Maxime Ripard <mripard@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>
Cc:     dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-amarula@...rulasolutions.com,
        Jagan Teki <jagan@...rulasolutions.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>
Subject: [PATCH v3 5/7] drm: bridge: Queue the bridge chain instead of stacking

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@...ux.intel.com>
Cc: Thomas Zimmermann <tzimmermann@...e.de>
Signed-off-by: Jagan Teki <jagan@...rulasolutions.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);
-- 
2.25.1