V4L/DVB (9357): cx88-dvb: Fix Oops in case i2c bus failed to register

There already is an report at kernel bugzilla about this issue:
http://bugzilla.kernel.org/show_bug.cgi?id=9455

When enabling extra checks for the i2c-bus of cx88 based cards by
loading i2c_algo_bit with bit_test=1 this may trigger an oops
when loading cx88_dvb.

This is caused by the extra check code that detects that the
sda-line is stuck high and thus does not register the i2c-bus.

cx88-dvb however does not check if the i2c-bus is valid and just
uses core->i2c_adap to attach dvb frontend modules.
This leads to an oops at the first call to i2c_transfer:

$ modprobe i2c_algo_bit bit_test=1
$ modprobe cx8802

cx88/2: cx2388x MPEG-TS Driver Manager version 0.0.6 loaded
cx88[0]: quirk: PCIPCI_NATOMA -- set TBFX
cx88[0]: subsystem: 0070:9202, board: Hauppauge Nova-S-Plus DVB-S [card=37,autodetected], frontend(s): 1
cx88[0]: TV tuner type 4, Radio tuner type -1
cx88[0]: SDA stuck high!
cx88[0]: i2c register FAILED
input: cx88 IR (Hauppauge Nova-S-Plus  as /class/input/input5
cx88[0]/2: cx2388x 8802 Driver Manager
cx88-mpeg driver manager 0000:00:10.2: enabling device (0154 -> 0156)
cx88-mpeg driver manager 0000:00:10.2: PCI INT A -> Link[LNKD] -> GSI 9 (level, low) -> IRQ 9
cx88[0]/2: found at 0000:00:10.2, rev: 5, irq: 9, latency: 64, mmio: 0xfb000000
cx8802_probe() allocating 1 frontend(s)
cx88/2: cx2388x dvb driver version 0.0.6 loaded
cx88/2: registering cx8802 driver, type: dvb access: shared
cx88[0]/2: subsystem: 0070:9202, board: Hauppauge Nova-S-Plus DVB-S [card=37]
cx88[0]/2: cx2388x based DVB/ATSC card
BUG: unable to handle kernel NULL pointer dereference at 00000000
IP: [<e084d4ef>] :i2c_core:i2c_transfer+0x1f/0x80
*pde = 00000000
Modules linked in: cx88_dvb(+) cx8802 cx88xx ir_common i2c_algo_bit tveeprom videobuf_dvb btcx_risc
mga drm ipv6 fscpos eeprom nfsd exportfs stv0299 b2c2_flexcop_pci b2c2_flexcop cx24123 s5h1420 ves1x93
dvb_ttpci dvb_core saa7146_vv saa7146 videobuf_dma_sg videobuf_core videodev v4l1_compat ttpci_eeprom
lirc_serial lirc_dev usbhid rtc uhci_hcd 8139too i2c_piix4 i2c_core usbcore evdev
Pid: 4249, comm: modprobe Not tainted (2.6.27-gentoo #3)
EIP: 0060:[<e084d4ef>] EFLAGS: 00010296 CPU: 0
EIP is at i2c_transfer+0x1f/0x80 [i2c_core]
EAX: 00000000 EBX: ffffffa1 ECX: 00000002 EDX: d6c71e3c
ESI: d80cd050 EDI: d8093c00 EBP: d6c71e20 ESP: d6c71e0c
DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 0068
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/cx88/cx88-dvb.c

@@ -598,6 +598,11 @@ static int dvb_register(struct cx8802_dev *dev)
 	struct videobuf_dvb_frontend *fe0, *fe1 = NULL;
 	int mfe_shared = 0; /* bus not shared by default */
 
+	if (0 != core->i2c_rc) {
+		printk(KERN_ERR "%s/2: no i2c-bus available, cannot attach dvb drivers\n", core->name);
+		goto frontend_detach;
+	}
+
 	/* Get the first frontend */
 	fe0 = videobuf_dvb_get_frontend(&dev->frontends, 1);
 	if (!fe0)