linux-kernel - [PATCH] drm/rockchip: Cope with endpoints that haven't been registered yet

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Message-ID: <20210316182753.GA25685@earth.li>
Date:   Tue, 16 Mar 2021 18:27:53 +0000
From:   Jonathan McDowell <noodles@...th.li>
To:     Sandy Huang <hjc@...k-chips.com>,
        Heiko Stübner <heiko@...ech.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] drm/rockchip: Cope with endpoints that haven't been
 registered yet

The Rockchip RGB CRTC output driver attempts to avoid probing Rockchip
subdrivers to see if they're a connected panel or bridge. However part
of its checks assumes that if no OF platform device is found then it
can't be a valid bridge or panel. This causes issues with I2C controlled
bridges that have not yet been registered to the point they can be
found.

Change this to return EPROBE_DEFER instead of ENODEV and don't ignore
such devices. The subsequent call to drm_of_find_panel_or_bridge() will
return EPROBE_DEFER as well if there's actually a valid device we should
wait for.

Signed-off-by: Jonathan McDowell <noodles@...th.li>
---
 drivers/gpu/drm/rockchip/rockchip_drm_drv.c | 8 ++++++--
 drivers/gpu/drm/rockchip/rockchip_rgb.c     | 7 ++++---
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
index 212bd87c0c4a..b0d63a566501 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
@@ -270,11 +270,15 @@ int rockchip_drm_endpoint_is_subdriver(struct device_node *ep)
 	if (!node)
 		return -ENODEV;
 
-	/* status disabled will prevent creation of platform-devices */
+	/*
+	 * status disabled will prevent creation of platform-devices,
+	 * but equally we can't rely on the driver having been registered
+	 * yet (e.g. I2C bridges).
+	 */
 	pdev = of_find_device_by_node(node);
 	of_node_put(node);
 	if (!pdev)
-		return -ENODEV;
+		return -EPROBE_DEFER;
 
 	/*
 	 * All rockchip subdrivers have probed at this point, so
diff --git a/drivers/gpu/drm/rockchip/rockchip_rgb.c b/drivers/gpu/drm/rockchip/rockchip_rgb.c
index c079714477d8..989595087397 100644
--- a/drivers/gpu/drm/rockchip/rockchip_rgb.c
+++ b/drivers/gpu/drm/rockchip/rockchip_rgb.c
@@ -77,7 +77,7 @@ struct rockchip_rgb *rockchip_rgb_init(struct device *dev,
 	struct drm_encoder *encoder;
 	struct device_node *port, *endpoint;
 	u32 endpoint_id;
-	int ret = 0, child_count = 0;
+	int subret, ret = 0, child_count = 0;
 	struct drm_panel *panel;
 	struct drm_bridge *bridge;
 
@@ -96,8 +96,9 @@ struct rockchip_rgb *rockchip_rgb_init(struct device *dev,
 		if (of_property_read_u32(endpoint, "reg", &endpoint_id))
 			endpoint_id = 0;
 
-		/* if subdriver (> 0) or error case (< 0), ignore entry */
-		if (rockchip_drm_endpoint_is_subdriver(endpoint) != 0)
+		/* if subdriver (> 0) or non-defer error case (< 0), ignore entry */
+		subret = rockchip_drm_endpoint_is_subdriver(endpoint);
+		if (subret != 0 && subret != -EPROBE_DEFER)
 			continue;
 
 		child_count++;
-- 
2.20.1