kernel since 5.6 do not boot anymore on Apple PowerBook

[Giuseppe Sacco]

Hello Christophe,

Il giorno lun, 24/08/2020 alle 07.17 +0200, Christophe Leroy ha
scritto:
> Hello Giuseppe,
[...]
> The Oopses in the video are fixed in 5.9-rc2, see my response to your 
> other mail.

Right, I just updated from git and rebuilt the kernel whith
CONFIG_VMAP_STACK not set and the machine boots correctly.

> So now we know that your kernel doesn't boot when CONFIG_VMAP_STACK is set.
> Can you remind the exact problem ?

latest kernel with CONFIG_VMAP_STACK set stops after writing:
pmac32_cpufreq: registering PowerMac CPU frequency driver
pmac32_cpufreq: Low: 667 MHz, High: 867 Mhz, Boot: 667 MHz

> One common problem with CONFIG_VMAP_STACK is when some drivers are 
> invalidly using buffers in stack for DMA.
> 
> Couldn't try with CONFIG_DEBUG_VIRTUAL (without CONFIG_VMAP_STACK) and 
> see if it triggers some warnings ?

I've just tried: it boots without any special warning. What should I
look for? This is an excerpt of dmesg output about the line it would
otherwise stop:

[...]
[    6.566984] PowerMac i2c bus pmu 2 registered
[    6.574879] PowerMac i2c bus pmu 1 registered
[    6.582634] PowerMac i2c bus mac-io 0 registered
[    6.590323] i2c i2c-2: No i2c address for /pci at f2000000/mac-io at 17/i2c at 18000/i2c-modem
[    6.598290] PowerMac i2c bus uni-n 1 registered
[    6.606196] i2c i2c-3: i2c-powermac: modalias failure on /uni-n at f8000000/i2c at f8001000/cereal at 1c0
[    6.614320] PowerMac i2c bus uni-n 0 registered
[    6.622501] pmac32_cpufreq: Registering PowerMac CPU frequency driver
[    6.630580] pmac32_cpufreq: Low: 667 Mhz, High: 867 Mhz, Boot: 667 Mhz
[    6.639518] ledtrig-cpu: registered to indicate activity on CPUs
[    6.647894] NET: Registered protocol family 10
[    6.656492] Segment Routing with IPv6
[    6.664490] mip6: Mobile IPv6
[    6.672337] NET: Registered protocol family 17
[    6.680213] mpls_gso: MPLS GSO support
[...]

Bye,
Giuseppe