media: ipu3-cio2: allow ipu_bridge to be a module again

This code was previously part of the VIDEO_IPU3_CIO2 driver, which could
be built-in or a loadable module, but after the move it turned into a
builtin-only driver. This fails to link when the I2C subsystem is a
module:

x86_64-linux-ld: drivers/media/pci/intel/ipu-bridge.o: in function `ipu_bridge_unregister_sensors':
ipu-bridge.c:(.text+0x50): undefined reference to `i2c_unregister_device'
x86_64-linux-ld: drivers/media/pci/intel/ipu-bridge.o: in function `ipu_bridge_init':
ipu-bridge.c:(.text+0x9c9): undefined reference to `i2c_acpi_new_device_by_fwnode'

In general, drivers should not have to be built-in, so change the option
to a tristate with the corresponding dependency. This in turn opens a
new problem with the dependency, as the IPU bridge can be a loadable module
while the ipu3 driver itself is built-in, producing a new link failure:

86_64-linux-ld: drivers/media/pci/intel/ipu3/ipu3-cio2.o: in function `cio2_pci_probe':
ipu3-cio2.c:(.text+0x197e): undefined reference to `ipu_bridge_init'

In order to fix this, restore the old Kconfig option that controlled
the ipu bridge driver before it was split out, but make it select a
hidden symbol that now corresponds to the bridge driver.

When other drivers get added that share ipu-bridge, this should cover
all corner cases, and allow any combination of them to be built-in
or modular.

Link: https://lore.kernel.org/linux-media/20230727122331.2421453-1-arnd@kernel.org

Fixes: 881ca259 ("media: ipu3-cio2: rename cio2 bridge to ipu bridge and move out of ipu3")'
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/pci/intel/Kconfig

 # SPDX-License-Identifier: GPL-2.0-only
 config IPU_BRIDGE
-	bool "Intel IPU Sensors Bridge"
-	depends on VIDEO_IPU3_CIO2 && ACPI
-	depends on I2C
+	tristate
+	depends on I2C && ACPI
 	help
-	  This extension provides an API for the Intel IPU driver to create
-	  connections to cameras that are hidden in the SSDB buffer in ACPI.
-	  It can be used to enable support for cameras in detachable / hybrid
-	  devices that ship with Windows.
-
-	  Say Y here if your device is a detachable / hybrid laptop that comes
-	  with Windows installed by the OEM, for example:
-
-		- Microsoft Surface models (except Surface Pro 3)
-		- The Lenovo Miix line (for example the 510, 520, 710 and 720)
-		- Dell 7285
-
-	  If in doubt, say N here.
+	  This is a helper module for the IPU bridge, which can be
+	  used by ipu3 and other drivers. In order to handle module
+	  dependencies, this is selected by each driver that needs it.
 
 source "drivers/media/pci/intel/ipu3/Kconfig"

drivers/media/pci/intel/ipu-bridge.c

@@ -493,3 +493,6 @@ int ipu_bridge_init(struct pci_dev *ipu)
 	return ret;
 }
 EXPORT_SYMBOL_NS_GPL(ipu_bridge_init, INTEL_IPU_BRIDGE);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Intel IPU Sensors Bridge driver");

drivers/media/pci/intel/ipu3/Kconfig

@@ -8,6 +8,7 @@ config VIDEO_IPU3_CIO2
 	select VIDEO_V4L2_SUBDEV_API
 	select V4L2_FWNODE
 	select VIDEOBUF2_DMA_SG
+	select IPU_BRIDGE if CIO2_BRIDGE
 
 	help
 	  This is the Intel IPU3 CIO2 CSI-2 receiver unit, found in Intel
@@ -17,3 +18,22 @@ config VIDEO_IPU3_CIO2
 	  Say Y or M here if you have a Skylake/Kaby Lake SoC with MIPI CSI-2
 	  connected camera.
 	  The module will be called ipu3-cio2.
+
+config CIO2_BRIDGE
+	bool "IPU3 CIO2 Sensors Bridge"
+	depends on VIDEO_IPU3_CIO2 && ACPI
+	depends on I2C
+	help
+	  This extension provides an API for the ipu3-cio2 driver to create
+	  connections to cameras that are hidden in the SSDB buffer in ACPI.
+	  It can be used to enable support for cameras in detachable / hybrid
+	  devices that ship with Windows.
+
+	  Say Y here if your device is a detachable / hybrid laptop that comes
+	  with Windows installed by the OEM, for example:
+
+		- Microsoft Surface models (except Surface Pro 3)
+		- The Lenovo Miix line (for example the 510, 520, 710 and 720)
+		- Dell 7285
+
+	  If in doubt, say N here.