Pi 4, 4GB RAM, not booting, CMA: failed to reserve 256 MiB mib.

[twobikes22]

New Pi 4, booted several times using buster full OK. Then in Raspberry Pi Config menu re allocated memory for GPU from 64 to 1024, dialog box returned 896 i think, left it at that also set hdmi port 0 to 60Hz, then rebooted.

Flash screen, 4 raspberry's, and following error messages:

[ 0.000000] cma: Failed to reserve 256 MiB
[ 0.220610] brcm-pcie fd500000.pcie: dmabounce: could not allocate 33554432 byte DMA pool
[ 0.220696] brcm-pcie fd500000.pcie: could not init bounce buffers: -12
[ 0.749793] [vc_sm_connected init]: failed to initialise CMA heap

Screen blanks out and nothing, also no USB port working or have power. No USB power worries me!

Any ideas? Have I faulty memory chip?

[twobikes22]

Sorted it out myself. Fortunately had enabled ssh, so ssh into pi, and edited /boot/config.txt, had the line gpu_mem=896, changed it to gpu_mem=256, saved and rebooted.

This fixed the usb ports and booted into gui. Begs the question why did it return 896, when i entered 1024 then corrupt the boot and usb ports on reboot?

What is the highest gpu_mem? 512, I tried 1024 for gui to insert 896. But does higher mem allocation help video performance? more play and pain will tell what the limits.

[kflmiami420]

try buster with desktop instead

[rpdom]

No point in putting GPU memory over 256MB. The new VC6 uses CMA to split memory between CPUS and GPU as required.

Even 256MB is possibly excessive.

[bensimmo]

Less and less will need the GPU allocation set aside.
Leave it at default unless it complains.

[twobikes22]

Thank you for the replies.

Learned that CMA stands for Contiguous Memory Allocation, this from a neat web site www.allacronyms.com, which will be my 1st place of call when I think what does ***** stand for? Yeah and back in the days I once thought LOL was Lots of Love.

Also learned that allocating more than 64 is not really going to help video performance, but hey I have got 4GB, so I think I will compromise at 128.

[bensimmo]

If you didn't find it
https://www.raspberrypi.org/forums/view ... 7&start=50
So we'll see how they get on with the big changes.
(And there is another roost somewhere)

[Towelie]

I am having the same issue. The difference is the software I run seems to check for available video memory and won't run if it is set to low.

The max I can seem to set it at is 512. Does anyone know of any way around this?

[scarlet_man]

Huge thanks to twobikes22 - this saved me.

Had the same problem, tried setting video memory to 1024 just - well - just for something to do

Next day found blank display on boot up...

Followed a slightly different process, not using SSH.

I happened to have another SD card with Raspbian on which came with the PI4 bundle, which I'd kept when I upgraded to 32GB. Was able to boot from this, then connect the usual SD card into a USB adaptor. Browsed to the SD and reset the line of config.txt as advised by twobikes22.

10 minute fix. Many thanks.

[simonliu]

In my Pi 4b 2GB RAM, I changed the gpu_mem=192 to gpu_mem =256, and it is working fine.