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Date:	Tue,  6 Oct 2015 14:54:40 +0530
From:	Archit Taneja <>
	Archit Taneja <>
Subject: [RFC v2 3/5] drm/dsi: Check for used channels

We don't check whether a previously registered mipi_dsi_device under the
same host shares the same virtual channel.

Before registering, check if any of the registered devices doesn't
already have the same virtual channel.

This wasn't crucial when all the devices under a host were populated via
DT. Now that we also support creating devices manually, we could end up
in a situation where a driver tries to create a device with a virtual
channel already taken by a device populated in DT.

Signed-off-by: Archit Taneja <>
 drivers/gpu/drm/drm_mipi_dsi.c | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
index 46ee515..db6130a 100644
--- a/drivers/gpu/drm/drm_mipi_dsi.c
+++ b/drivers/gpu/drm/drm_mipi_dsi.c
@@ -123,6 +123,22 @@ static const struct device_type mipi_dsi_device_type = {
 	.release = mipi_dsi_dev_release,
+static int __dsi_check_chan_busy(struct device *dev, void *data)
+	struct mipi_dsi_device *dsi = to_mipi_dsi_device(dev);
+	u32 reg = *(u32 *) data;
+	if (dsi && dsi->channel == reg)
+		return -EBUSY;
+	return 0;
+static int mipi_dsi_check_chan_busy(struct mipi_dsi_host *host, u32 reg)
+	return device_for_each_child(host->dev, &reg, __dsi_check_chan_busy);
 struct mipi_dsi_device *mipi_dsi_device_new(struct mipi_dsi_host *host,
 					    struct mipi_dsi_device_info *info)
@@ -150,14 +166,20 @@ struct mipi_dsi_device *mipi_dsi_device_new(struct mipi_dsi_host *host,
 	dev_set_name(&dsi->dev, "%s.%d", dev_name(host->dev), info->reg);
+	r = mipi_dsi_check_chan_busy(host, info->reg);
+	if (r)
+		goto err;
 	r = device_register(&dsi->dev);
 	if (r) {
 		dev_err(dev, "failed to register device: %d\n", r);
-		kfree(dsi);
-		return ERR_PTR(r);
+		goto err;
 	return dsi;
+	kfree(dsi);
+	return ERR_PTR(r);
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