RPi3 kernel CONFIG_VMSPLIT_3G

[peyo]

For some applications, I need user/kernel address split of 3G/1G - rather than default 2G/2G.

Until RPi2, modifying kernel source's (github.com/raspberrypi/linux) bcm2709_defconfig
from CONFIG_VMSPLIT_2G to CONFIG_VMSPLIT_3G, and recompiling the kernel - works fine.

On RPi3, modifying it blocks kernel booting. With VMSPLIT_2G, kernel & OS are working fine.
But with VMSPLIT_3G, kernel shows nothing on HDMI output neither on serial console.

I have tried a few branches - rpi-4.1.y / rpi-4.2.y / rpi-4.5.y - and results were same.
Device tree files were bcm2709-rpi-2-b.dtb & bcm2710-rpi-3-b.dtb for matched RPi boards,
just have been re-built, not modified from the github source.

Does anyone have understanding on this ?

[phelum]

Hi,

No answer or even an explanation but I hit the same problem. 2G/2G is the only split that works. I'd also be interested to know why.

Cheers,
Steven

[edge0f17]

CONFIG_VMSPLIT is used to set the physical address of the RAM, so you have to use the "right" setting. That might be a kernel "bug" that could be fixed.

[peyo]

Solution found by posting an issue on github :
https://github.com/raspberrypi/linux/issues/1394

[springyulei]

Hey, i have check the github issues discussion, I still do not quite know how to do this. Could anyone provide more details. Thanks