Hi, Saravana,

On 12/18/20 5:17 AM, Saravana Kannan wrote:
> Cyclic dependencies in some firmware was one of the last remaining
> reasons fw_devlink=on couldn't be set by default. Now that cyclic
> dependencies don't block probing, set fw_devlink=on by default.
> 
> Setting fw_devlink=on by default brings a bunch of benefits (currently,
> only for systems with device tree firmware):
> * Significantly cuts down deferred probes.
> * Device probe is effectively attempted in graph order.
> * Makes it much easier to load drivers as modules without having to
>   worry about functional dependencies between modules (depmod is still
>   needed for symbol dependencies).
> 
> If this patch prevents some devices from probing, it's very likely due
> to the system having one or more device drivers that "probe"/set up a
> device (DT node with compatible property) without creating a struct
> device for it.  If we hit such cases, the device drivers need to be
> fixed so that they populate struct devices and probe them like normal
> device drivers so that the driver core is aware of the devices and their
> status. See [1] for an example of such a case.
> 
> [1] - https://lore.kernel.org/lkml/CAGETcx9PiX==mLxB9PO8Myyk6u2vhPVwTMsA5NkD-ywH5xhusw@mail.gmail.com/
> Signed-off-by: Saravana Kannan <saravanak@google.com>

next-20210125 fails to boot on at91 sama5d2 platforms. No output is
seen, unless earlyprintk is enabled.

I have bisected this to commit e590474768f1cc04 ("driver core: Set
fw_devlink=on by default").

I've attached a log that I'm seeing on a sama5d2_xplained (sama5_defconfig
and arch/arm/boot/dts/at91-sama5d2_xplained.dts). I enabled the
following logs:
1. The ones in device_links_check_suppliers()
2. The ones in device_link_add()
3. initcall_debug=1

There seem to be some probe fails due to the pmc supplier not being ready:
calling  at_xdmac_init+0x0/0x18 @ 1                                             
platform f0010000.dma-controller: probe deferral - supplier f0014000.pmc not ready
platform f0004000.dma-controller: probe deferral - supplier f0014000.pmc not ready
initcall at_xdmac_init+0x0/0x18 returned -19 after 19531 usecs  

calling  udc_driver_init+0x0/0x18 @ 1
platform 300000.gadget: probe deferral - supplier f0014000.pmc not ready
initcall udc_driver_init+0x0/0x18 returned -19 after 7524 usecs

There are others too. I'm checking them.

Cheers,
ta