Kernel oops when syncing (and can't use reusable)

[iabdalkader]

First I wanted to thank you for this module I find it very useful and exactly what I need for my project. That said, I'm seeing the exact same issue reported in #10 (kernel oops when sync'ing with reserved memory and no-map;). I tired using reusable; as you suggested, but I get an error when loading udmabuf.

device tree:

reserved-memory {
    #address-cells = <1>;
    #size-cells = <1>;
    ranges;

    fb: fb@0 {
        compatible = "shared-dma-pool";
        reg = <0xd8000000 0x100000>;
        label = "fb";
        reusable;
    };
};

udmabuf@0 {
    compatible = "ikwzm,u-dma-buf";
    device-name = "fb";
    minor-number = <0>;
    memory-region = <&fb>;
    size = <0x100000>; // 1MiB
};

When doing modprobe u-dma-buf:

[   16.367839] u_dma_buf: loading out-of-tree module taints kernel.
[   16.370110] u-dma-buf udmabuf@0: of_reserved_mem_device_init failed. return=-22
[   16.370380] u-dma-buf udmabuf@0: driver installed.
[   16.370403] u-dma-buf: probe of udmabuf@0 failed with error -22

I also noticed the memory is not actually reserved with reusable :

cat /proc/iomem
.....
d8000000-dfffffff : System RAM

It must be part of some memory pool. When using no-map I can see it's reserved:

cat /pro/iomem
....
d8100000-dfffffff : System RAM

I'm testing on ARM + kernel 4.19.49... Any suggestions to fix this ? I need to use reserve memory so the address is known, and be able to invalidate the cache after a DMA write...

[ikwzm]

Thank you for the issue.

The Linux CMA region has alignment constraints. For MPSoC, the address and size that can be specified in the regs property of reserved-memory must be in units of 0x00400000 (4MiB).

Please also refer to this issue.

https://github.com/ikwzm/udmabuf/issues/29

[iabdalkader]

You were right, I fixed the alignment issue (in my case had to reserve 8MBytes) and it's now working. Thanks for the help.