Re: [PATCH] clk: Mark fwnodes when their clock provider is added

[Stephen Boyd]

Quoting Nicolas Saenz Julienne (2021-03-25 11:25:24)
> On Thu, 2021-03-25 at 14:31 +0100, Marek Szyprowski wrote:
> > Hi
> > 
> > On 10.02.2021 12:44, Tudor Ambarus wrote:
> > > This is a follow-up for:
> > > commit 3c9ea42802a1 ("clk: Mark fwnodes when their clock provider is added/removed")
> > > 
> > > The above commit updated the deprecated of_clk_add_provider(),
> > > but missed to update the preferred of_clk_add_hw_provider().
> > > Update it now.
> > > 
> > > Signed-off-by: Tudor Ambarus <tudor.ambarus@xxxxxxxxxxxxx>
> > 
> > This patch, which landed in linux-next as commit 6579c8d97ad7 ("clk: 
> > Mark fwnodes when their clock provider is added") causes the following 
> > NULL pointer dereference on Raspberry Pi 3b+ boards:
> > 
> > --->8---
> > 
> > raspberrypi-firmware soc:firmware: Attached to firmware from 
> > 2020-01-06T13:05:25
> > Unable to handle kernel NULL pointer dereference at virtual address 
> > 0000000000000050
> > Mem abort info:
> >    ESR = 0x96000004
> >    EC = 0x25: DABT (current EL), IL = 32 bits
> >    SET = 0, FnV = 0
> >    EA = 0, S1PTW = 0
> > Data abort info:
> >    ISV = 0, ISS = 0x00000004
> >    CM = 0, WnR = 0
> > [0000000000000050] user address but active_mm is swapper
> > Internal error: Oops: 96000004 [#1] PREEMPT SMP
> > Modules linked in:
> > CPU: 0 PID: 10 Comm: kworker/0:1 Not tainted 5.12.0-rc4+ #2764
> > Hardware name: Raspberry Pi 3 Model B (DT)
> > Workqueue: events deferred_probe_work_func
> > pstate: 00000005 (nzcv daif -PAN -UAO -TCO BTYPE=--)
> > pc : of_clk_add_hw_provider+0xac/0xe8
> > lr : of_clk_add_hw_provider+0x94/0xe8
> > sp : ffff8000130936b0
> > x29: ffff8000130936b0 x28: ffff800012494e04
> > x27: ffff00003b18cb05 x26: ffff00003aa5c010
> > x25: 0000000000000000 x24: 0000000000000000
> > x23: ffff00003aa1e380 x22: ffff8000106830d0
> > x21: ffff80001233f180 x20: 0000000000000018
> > x19: 0000000000000000 x18: ffff8000124d38b0
> > x17: 0000000000000013 x16: 0000000000000014
> > x15: ffff8000125758b0 x14: 00000000000184e0
> > x13: 000000000000292e x12: ffff80001258dd98
> > x11: 0000000000000001 x10: 0101010101010101
> > x9 : ffff80001233f288 x8 : 7f7f7f7f7f7f7f7f
> > x7 : fefefefeff6c626f x6 : 5d636d8080808080
> > x5 : 00000000006d635d x4 : 0000000000000000
> > x3 : 0000000000000000 x2 : 540eb5edae191600
> > x1 : 0000000000000000 x0 : 0000000000000000
> > Call trace:
> >   of_clk_add_hw_provider+0xac/0xe8
> >   devm_of_clk_add_hw_provider+0x5c/0xb8
> >   raspberrypi_clk_probe+0x110/0x210
> >   platform_probe+0x90/0xd8
> >   really_probe+0x108/0x3c0
> >   driver_probe_device+0x60/0xc0
> >   __device_attach_driver+0x9c/0xd0
> >   bus_for_each_drv+0x70/0xc8
> >   __device_attach+0xec/0x150
> >   device_initial_probe+0x10/0x18
> >   bus_probe_device+0x94/0xa0
> >   device_add+0x47c/0x780
> >   platform_device_add+0x110/0x248
> >   platform_device_register_full+0x120/0x150
> >   rpi_firmware_probe+0x158/0x1f8
> >   platform_probe+0x90/0xd8
> >   really_probe+0x108/0x3c0
> >   driver_probe_device+0x60/0xc0
> >   __device_attach_driver+0x9c/0xd0
> >   bus_for_each_drv+0x70/0xc8
> >   __device_attach+0xec/0x150
> >   device_initial_probe+0x10/0x18
> >   bus_probe_device+0x94/0xa0
> >   deferred_probe_work_func+0x70/0xa8
> >   process_one_work+0x2a8/0x718
> >   worker_thread+0x48/0x460
> >   kthread+0x134/0x160
> >   ret_from_fork+0x10/0x18
> > Code: b1006294 540000c0 b140069f 54000088 (3940e280)
> > ---[ end trace 7ead5ec2f0c51cfe ]---
> > 
> > This patch mainly revealed that clk/bcm/clk-raspberrypi.c driver calls 
> > devm_of_clk_add_hw_provider(), with a device pointer, which has a NULL 
> > dev->of_node. I'm not sure if adding a check for a NULL np in 
> > of_clk_add_hw_provider() is a right fix, though.
> 
> I believe the right fix is not to call 'devm_of_clk_add_hw_provider()' if
> 'pdev->dev.of_node == NULL'. In such case, which is RPi3's, only the CPU clock
> is used, and it's defined and queried later through
> devm_clk_hw_register_clkdev().
> 
> @Marek, I don't mind taking care of it if it's OK with you.
> 

Ah I see this is related to the patch I just reviewed. Can you reference
this in the commit text? And instead of putting the change into the clk
provider let's check for NULL 'np' in of_clk_add_hw_provider() instead
and return 0 if there's nothing to do. That way we don't visit this
problem over and over again.