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From:   Maxime Ripard <maxime@cerno.tech>
To:     Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
        Eric Anholt <eric@anholt.net>
Cc:     dri-devel@lists.freedesktop.org,
        linux-rpi-kernel@lists.infradead.org,
        bcm-kernel-feedback-list@broadcom.com,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Dave Stevenson <dave.stevenson@raspberrypi.com>,
        Tim Gover <tim.gover@raspberrypi.com>,
        Phil Elwell <phil@raspberrypi.com>,
        Andrzej Hajda <a.hajda@samsung.com>,
        Maxime Ripard <maxime@cerno.tech>
Subject: [PATCH] drm/vc4: dsi: Only register our component once a DSI device is attached
Date:   Tue,  7 Jul 2020 12:19:12 +0200
Message-Id: <20200707101912.571531-1-maxime@cerno.tech>
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

If the DSI driver is the last to probe, component_add will try to run all
the bind callbacks straight away and return the error code.

However, since we depend on a power domain, we're pretty much guaranteed to
be in that case on the BCM2711, and are just lucky on the previous SoCs
since the v3d also depends on that power domain and is further in the probe
order.

In that case, the DSI host will not stick around in the system: the DSI
bind callback will be executed, will not find any DSI device attached and
will return EPROBE_DEFER, and we will then remove the DSI host and ask to
be probed later on.

But since that host doesn't stick around, DSI devices like the RaspberryPi
touchscreen whose probe is not linked to the DSI host (unlike the usual DSI
devices that will be probed through the call to mipi_dsi_host_register)
cannot attach to the DSI host, and we thus end up in a situation where the
DSI host cannot probe because the panel hasn't probed yet, and the panel
cannot probe because the DSI host hasn't yet.

In order to break this cycle, let's wait until there's a DSI device that
attaches to the DSI host to register the component and allow to progress
further.

Suggested-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
---
 drivers/gpu/drm/vc4/vc4_dsi.c | 25 ++++++++-----------------
 1 file changed, 8 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
index eaf276978ee7..19aab4e7e209 100644
--- a/drivers/gpu/drm/vc4/vc4_dsi.c
+++ b/drivers/gpu/drm/vc4/vc4_dsi.c
@@ -1246,10 +1246,12 @@ static ssize_t vc4_dsi_host_transfer(struct mipi_dsi_host *host,
 	return ret;
 }
 
+static const struct component_ops vc4_dsi_ops;
 static int vc4_dsi_host_attach(struct mipi_dsi_host *host,
 			       struct mipi_dsi_device *device)
 {
 	struct vc4_dsi *dsi = host_to_dsi(host);
+	int ret;
 
 	dsi->lanes = device->lanes;
 	dsi->channel = device->channel;
@@ -1284,6 +1286,12 @@ static int vc4_dsi_host_attach(struct mipi_dsi_host *host,
 		return 0;
 	}
 
+	ret = component_add(&dsi->pdev->dev, &vc4_dsi_ops);
+	if (ret) {
+		mipi_dsi_host_unregister(&dsi->dsi_host);
+		return ret;
+	}
+
 	return 0;
 }
 
@@ -1662,7 +1670,6 @@ static int vc4_dsi_dev_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	struct vc4_dsi *dsi;
-	int ret;
 
 	dsi = devm_kzalloc(dev, sizeof(*dsi), GFP_KERNEL);
 	if (!dsi)
@@ -1670,26 +1677,10 @@ static int vc4_dsi_dev_probe(struct platform_device *pdev)
 	dev_set_drvdata(dev, dsi);
 
 	dsi->pdev = pdev;
-
-	/* Note, the initialization sequence for DSI and panels is
-	 * tricky.  The component bind above won't get past its
-	 * -EPROBE_DEFER until the panel/bridge probes.  The
-	 * panel/bridge will return -EPROBE_DEFER until it has a
-	 * mipi_dsi_host to register its device to.  So, we register
-	 * the host during pdev probe time, so vc4 as a whole can then
-	 * -EPROBE_DEFER its component bind process until the panel
-	 * successfully attaches.
-	 */
 	dsi->dsi_host.ops = &vc4_dsi_host_ops;
 	dsi->dsi_host.dev = dev;
 	mipi_dsi_host_register(&dsi->dsi_host);
 
-	ret = component_add(&pdev->dev, &vc4_dsi_ops);
-	if (ret) {
-		mipi_dsi_host_unregister(&dsi->dsi_host);
-		return ret;
-	}
-
 	return 0;
 }
 
-- 
2.26.2