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SubjectRe: [RFC PATCH net-next 4/9] net: pcs: lynx: Convert to an mdio driver
On Mon, Jul 11, 2022 at 12:05:14PM -0400, Sean Anderson wrote:
> This converts the lynx PCS driver to a proper MDIO driver. This allows
> using a more conventional driver lifecycle (e.g. with a probe and
> remove). For compatibility with existing device trees lacking a
> compatible property, we bind the driver in lynx_pcs_create. This is
> intended only as a transitional method. After compatible properties are
> added to all existing device trees (and a reasonable amount of time has
> passed), then lynx_pcs_create can be removed, and users can be converted
> to pcs_get_fwnode.
>
> Signed-off-by: Sean Anderson <sean.anderson@seco.com>
> ---

I'm compiling and testing patch by patch now. Here's how things go on
LS1028A at this stage:

[ 6.317357] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000110
[ 6.326219] Mem abort info:
[ 6.329027] ESR = 0x0000000096000004
[ 6.332815] EC = 0x25: DABT (current EL), IL = 32 bits
[ 6.338182] SET = 0, FnV = 0
[ 6.341252] EA = 0, S1PTW = 0
[ 6.344436] FSC = 0x04: level 0 translation fault
[ 6.349378] Data abort info:
[ 6.352273] ISV = 0, ISS = 0x00000004
[ 6.356154] CM = 0, WnR = 0
[ 6.359164] [0000000000000110] user address but active_mm is swapper
[ 6.365629] Internal error: Oops: 96000004 [#1] PREEMPT SMP
[ 6.371221] Modules linked in:
[ 6.374284] CPU: 1 PID: 8 Comm: kworker/u4:0 Not tainted 5.19.0-rc6-07010-ga9b9500ffaac-dirty #3317
[ 6.383364] Hardware name: LS1028A RDB Board (DT)
[ 6.388081] Workqueue: events_unbound deferred_probe_work_func
[ 6.393939] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 6.400926] pc : __driver_probe_device+0x1c/0x150
[ 6.405646] lr : device_driver_attach+0x58/0xc0
[ 6.410190] sp : ffff8000085639c0
[ 6.413510] x29: ffff8000085639c0 x28: ffffb1a2587dae50 x27: ffff2b6943304bc0
[ 6.420676] x26: ffff2b694330c000 x25: ffff2b69433010a0 x24: ffff2b69bf719898
[ 6.427840] x23: ffff2b6941074000 x22: ffff2b6943304000 x21: ffff2b6943301880
[ 6.435004] x20: ffff2b6943301800 x19: ffffb1a259faf3d0 x18: ffffffffffffffff
[ 6.442168] x17: 000000002b64f81b x16: 000000006d50a0b2 x15: ffff2b6943307196
[ 6.449332] x14: 0000000000000002 x13: ffff2b6943307194 x12: 0000000000000003
[ 6.456497] x11: ffff2b69433018f0 x10: 0000000000000003 x9 : ffffb1a2578b1e08
[ 6.463662] x8 : ffff2b6940b36200 x7 : ffffb1a25a0da000 x6 : 000000003225858e
[ 6.470826] x5 : 0000000000000000 x4 : ffff79c76227a000 x3 : 0000000000000000
[ 6.477989] x2 : 0000000000000000 x1 : ffff2b6943301800 x0 : ffffb1a259faf3d0
[ 6.485153] Call trace:
[ 6.487601] __driver_probe_device+0x1c/0x150
[ 6.491971] device_driver_attach+0x58/0xc0
[ 6.496167] lynx_pcs_create+0x30/0x7c
[ 6.499927] enetc_pf_probe+0x984/0xeb0
[ 6.503775] local_pci_probe+0x4c/0xc0
[ 6.507536] pci_device_probe+0xb8/0x210
[ 6.511470] really_probe.part.0+0xa4/0x2b0
[ 6.515665] __driver_probe_device+0xa0/0x150
[ 6.520033] driver_probe_device+0xb4/0x150
[ 6.524228] __device_attach_driver+0xc4/0x130
[ 6.528684] bus_for_each_drv+0x84/0xe0
[ 6.532529] __device_attach+0xb0/0x1d0
[ 6.536375] device_initial_probe+0x20/0x2c
[ 6.540569] bus_probe_device+0xac/0xb4
[ 6.544414] deferred_probe_work_func+0x98/0xd4
[ 6.548956] process_one_work+0x294/0x6d0
[ 6.552979] worker_thread+0x80/0x460
[ 6.556651] kthread+0x124/0x130
[ 6.559887] ret_from_fork+0x10/0x20
[ 6.563475] Code: a9bd7bfd 910003fd a90153f3 f9402422 (39444042)

Disassembly of drivers/base/dd.c shows that dev->p is a NULL pointer,
and dev->p->dead goes right through it. How did we even get here...
device_private_init() should be called by device_add().

Curiously enough, mdio_device_create() only calls device_initialize().
It's mdio_device_register() that calls device_add(). So after this
patch, we cannot call lynx_pcs_create() without calling
mdio_device_register().

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