[PATCH v2] drm/bridge: megachips: Fix error handling in i2c_register_driver()

[Yuan Can]

A problem about insmod megachips-stdpxxxx-ge-b850v3-fw.ko failed is
triggered with the following log given:

[ 4497.981497] Error: Driver 'stdp4028-ge-b850v3-fw' is already registered, aborting...
insmod: ERROR: could not insert module megachips-stdpxxxx-ge-b850v3-fw.ko: Device or resource busy

The reason is that stdpxxxx_ge_b850v3_init() returns i2c_add_driver()
directly without checking its return value, if i2c_add_driver() failed,
it returns without calling i2c_del_driver() on the previous i2c driver,
resulting the megachips-stdpxxxx-ge-b850v3-fw can never be installed
later.
A simple call graph is shown as below:

 stdpxxxx_ge_b850v3_init()
   i2c_add_driver(&stdp4028_ge_b850v3_fw_driver)
   i2c_add_driver(&stdp2690_ge_b850v3_fw_driver)
     i2c_register_driver()
       driver_register()
         bus_add_driver()
           priv = kzalloc(...) # OOM happened
   # return without delete stdp4028_ge_b850v3_fw_driver

Fix by calling i2c_del_driver() on stdp4028_ge_b850v3_fw_driver when
i2c_add_driver() returns error.

Fixes: fcfa0ddc18ed ("drm/bridge: Drivers for megachips-stdpxxxx-ge-b850v3-fw (LVDS-DP++)")
Signed-off-by: Yuan Can <yuancan at huawei.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda at intel.com>
---
Changes in v2:
- Add Andrzej's Reviewed-by
- Change to the new error return style suggested by Andrzej

 drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c b/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
index 97359f807bfc..cbfa05a6767b 100644
--- a/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
+++ b/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
@@ -440,7 +440,11 @@ static int __init stdpxxxx_ge_b850v3_init(void)
 	if (ret)
 		return ret;
 
-	return i2c_add_driver(&stdp2690_ge_b850v3_fw_driver);
+	ret = i2c_add_driver(&stdp2690_ge_b850v3_fw_driver);
+	if (ret)
+		i2c_del_driver(&stdp4028_ge_b850v3_fw_driver);
+
+	return ret;
 }
 module_init(stdpxxxx_ge_b850v3_init);
 
-- 
2.17.1