Commit ee873fda



    "gianfar: Pack struct gfar_priv_grp into three cachelines"

causes the following null dereference at driver init on sbc8548:

   libphy: Freescale PowerQUICC MII Bus: probed
   Unable to handle kernel paging request for data at address 0x00000000
   Faulting instruction address: 0xc01d6a38
   Oops: Kernel access of bad area, sig: 11 [#1]
   [...]
   NIP [c01d6a38] gfar_parse_group+0x228/0x280
   LR [c01d6a34] gfar_parse_group+0x224/0x280
   Call Trace:
   [ef82dd60] [c01d6a34] gfar_parse_group+0x224/0x280 (unreliable)
   [ef82dd90] [c01d73a4] gfar_probe+0x284/0xfe0

The reason is that the commit also changed the allocation of the
Rx and error handling irq structs to be skipped for !MQ_MG_MODE.
In the !MQ_MG_MODE case, only the Tx irq struct is allocated.

Digging further, we see that MQ_MG_MODE is set only if we find
the OF compatible string "fsl,etsec2".

A quick grep in the dts directory shows lots of boards that support
Rx/Tx/Err, but without this specific compat string.  And hence they
go after the unallocated Rx/Error structs and cause the above oops.

Hence such a change can not be deployed until all the dts files
are updated and sufficiently deployed.  Further, the optimization
is of limited value, since the kmalloc'd struct in question has only
a single unsigned int, and an (IFNAMSIZ + 6) sized string.

Note that no changes to the freeing code are needed here, as it
already did an unconditional free of Rx/Tx/Error gfar_irqinfo.

Cc: Claudiu Manoil <claudiu.manoil@freescale.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>