When a PMIC is not found, this driver is unable to obtain its
'vdds_dsi_reg' regulator.  Even through its initialization function
fails, other code still calls its enable function, which fails to
check whether it has this regulator before asking for it to be enabled.

This fixes the oops, however a better fix would be to sort out the
upper layers to prevent them calling into a module which failed to
initialize.

Unable to handle kernel NULL pointer dereference at virtual address 00000038
pgd = c0004000
[00000038] *pgd=00000000
Internal error: Oops: 5 [#1] PREEMPT
Modules linked in:
CPU: 0    Not tainted  (3.3.0-rc2+ #228)
PC is at regulator_enable+0x10/0x70
LR is at omapdss_dpi_display_enable+0x54/0x15c
pc : [<c01b9a08>]    lr : [<c01af994>]    psr: 60000013
sp : c181fd90  ip : c181fdb0  fp : c181fdac
r10: c042eff0  r9 : 00000060  r8 : c044a164
r7 : c042c0e4  r6 : c042bd60  r5 : 00000000  r4 : c042bd60
r3 : c084de48  r2 : c181e000  r1 : c042bd60  r0 : 00000000
Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment kernel
Control: 10c5387d  Table: 80004019  DAC: 00000015
Process swapper (pid: 1, stack limit = 0xc181e2e8)
Stack: (0xc181fd90 to 0xc1820000)
fd80:                                     c001754c c042bd60 00000000 c042bd60
fda0: c181fdcc c181fdb0 c01af994 c01b9a04 c0016104 c042bd60 c042bd60 c044a338
fdc0: c181fdec c181fdd0 c01b5ed0 c01af94c c042bd60 c042bd60 c1aa8000 c1aa8a0c
fde0: c181fe04 c181fdf0 c01b5f54 c01b5ea8 c02fc18c c042bd60 c181fe3c c181fe08
fe00: c01b2a18 c01b5f48 c01aed14 c02fc160 c01df8ec 00000002 c042bd60 00000003
fe20: c042bd60 c1aa8000 c1aa8a0c c042eff8 c181fe84 c181fe40 c01b3874 c01b29fc
fe40: c042eff8 00000000 c042f000 c0449db8 c044ed78 00000000 c181fe74 c042eff8
fe60: c042eff8 c0449db8 c0449db8 c044ed78 00000000 00000000 c181fe94 c181fe88
fe80: c01e452c c01b35e8 c181feb4 c181fe98 c01e2fdc c01e4518 c042eff8 c0449db8
fea0: c0449db8 c181fef0 c181fecc c181feb8 c01e3104 c01e2f48 c042eff8 c042f02c
fec0: c181feec c181fed0 c01e3190 c01e30c0 c01e311c 00000000 c01e311c c0449db8
fee0: c181ff14 c181fef0 c01e1998 c01e3128 c18330a8 c1892290 c04165e8 c0449db8
ff00: c0449db8 c1ab60c0 c181ff24 c181ff18 c01e2e28 c01e194c c181ff54 c181ff28
ff20: c01e2218 c01e2e14 c039afed c181ff38 c04165e8 c041660c c0449db8 00000013
ff40: 00000000 c03ffdb8 c181ff7c c181ff58 c01e384c c01e217c c181ff7c c04165e8
ff60: c041660c c003a37c 00000013 00000000 c181ff8c c181ff80 c01e488c c01e3790
ff80: c181ff9c c181ff90 c03ffdcc c01e484c c181ffdc c181ffa0 c0008798 c03ffdc4
ffa0: c181ffc4 c181ffb0 c0056440 c0187810 c003a37c c04165e8 c041660c c003a37c
ffc0: 00000013 00000000 00000000 00000000 c181fff4 c181ffe0 c03ea284 c0008708
ffe0: 00000000 c03ea208 00000000 c181fff8 c003a37c c03ea214 1073cec0 01f7ee08
Backtrace:
[<c01b99f8>] (regulator_enable+0x0/0x70) from [<c01af994>] (omapdss_dpi_display_enable+0x54/0x15c)
 r6:c042bd60 r5:00000000 r4:c042bd60
[<c01af940>] (omapdss_dpi_display_enable+0x0/0x15c) from [<c01b5ed0>] (generic_dpi_panel_power_on+0x34/0x78)
 r6:c044a338 r5:c042bd60 r4:c042bd60
[<c01b5e9c>] (generic_dpi_panel_power_on+0x0/0x78) from [<c01b5f54>] (generic_dpi_panel_enable+0x18/0x28)
 r7:c1aa8a0c r6:c1aa8000 r5:c042bd60 r4:c042bd60
[<c01b5f3c>] (generic_dpi_panel_enable+0x0/0x28) from [<c01b2a18>] (omapfb_init_display+0x28/0x150)
 r4:c042bd60
[<c01b29f0>] (omapfb_init_display+0x0/0x150) from [<c01b3874>] (omapfb_probe+0x298/0x318)
 r8:c042eff8 r7:c1aa8a0c r6:c1aa8000 r5:c042bd60 r4:00000003
[<c01b35dc>] (omapfb_probe+0x0/0x318) from [<c01e452c>] (platform_drv_probe+0x20/0x24)
[<c01e450c>] (platform_drv_probe+0x0/0x24) from [<c01e2fdc>] (really_probe+0xa0/0x178)
[<c01e2f3c>] (really_probe+0x0/0x178) from [<c01e3104>] (driver_probe_device+0x50/0x68)
 r7:c181fef0 r6:c0449db8 r5:c0449db8 r4:c042eff8
[<c01e30b4>] (driver_probe_device+0x0/0x68) from [<c01e3190>] (__driver_attach+0x74/0x98)
 r5:c042f02c r4:c042eff8
[<c01e311c>] (__driver_attach+0x0/0x98) from [<c01e1998>] (bus_for_each_dev+0x58/0x98)
 r6:c0449db8 r5:c01e311c r4:00000000
[<c01e1940>] (bus_for_each_dev+0x0/0x98) from [<c01e2e28>] (driver_attach+0x20/0x28)
 r7:c1ab60c0 r6:c0449db8 r5:c0449db8 r4:c04165e8
[<c01e2e08>] (driver_attach+0x0/0x28) from [<c01e2218>] (bus_add_driver+0xa8/0x22c)
[<c01e2170>] (bus_add_driver+0x0/0x22c) from [<c01e384c>] (driver_register+0xc8/0x154)
[<c01e3784>] (driver_register+0x0/0x154) from [<c01e488c>] (platform_driver_register+0x4c/0x60)
 r8:00000000 r7:00000013 r6:c003a37c r5:c041660c r4:c04165e8
[<c01e4840>] (platform_driver_register+0x0/0x60) from [<c03ffdcc>] (omapfb_init+0x14/0x34)
[<c03ffdb8>] (omapfb_init+0x0/0x34) from [<c0008798>] (do_one_initcall+0x9c/0x164)
[<c00086fc>] (do_one_initcall+0x0/0x164) from [<c03ea284>] (kernel_init+0x7c/0x120)
[<c03ea208>] (kernel_init+0x0/0x120) from [<c003a37c>] (do_exit+0x0/0x2d8)
 r5:c03ea208 r4:00000000
Code: e1a0c00d e92dd870 e24cb004 e24dd004 (e5906038)
---[ end trace 9e2474c2e193b223 ]---

Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>