On Thu, Oct 24, 2019 at 9:22 AM Ayan Halder <Ayan.Halder@xxxxxxx> wrote:
>
>
> Hi Folks,
>
> I have a question regarding "reserved-memory". I am using an Arm Juno
> platform which has a chunk of ram in its fpga. I intend to make this
> memory as reserved so that it can be shared between various devices
> for passing framebuffer.
>
> My dts looks like the following:-
>
> / {
> .... // some nodes
>
> tlx@60000000 {
> compatible = "simple-bus";
> ...
>
> juno_wrapper {
>
> ... /* here we have all the nodes */
> /* corresponding to the devices in the fpga */
>
> memory@d000000 {
> device_type = "memory";
> reg = <0x00 0x60000000 0x00 0x8000000>;
> };
>
> reserved-memory {
> #address-cells = <0x01>;
> #size-cells = <0x01>;
> ranges;
>
> framebuffer@d000000 {
> compatible = "shared-dma-pool";
> linux,cma-default;
> reusable;
> reg = <0x00 0x60000000 0x00 0x8000000>;
> phandle = <0x44>;
> };
> };
> ...
> }
> }
> ...
> }
>
> Note that the depth of the "reserved-memory" node is 3.
>
> Refer __fdt_scan_reserved_mem() :-
>
> if (!found && depth == 1 && strcmp(uname, "reserved-memory") == 0) {
>
> if (__reserved_mem_check_root(node) != 0) {
> pr_err("Reserved memory: unsupported node
> format, ignoring\n");
> /* break scan */
> return 1;
> }
> found = 1;
>
> /* scan next node */
> return 0;
> }
>
> It expects the "reserved-memory" node to be at depth == 1 and so it
> does not probe it in our case.
>
> Niether from the
> Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> nor from commit - e8d9d1f5485b52ec3c4d7af839e6914438f6c285,
> I could understand the reason for such restriction.
>
> So, I seek the community's advice as to whether I should fix up
> __fdt_scan_reserved_mem() so as to do away with the restriction or
> put the "reserved-memory" node outside of 'tlx@60000000' (which looks
> logically incorrect as the memory is on the fpga platform).
For now, I'm going to say it must be at the root level. I'd guess the
memory@d000000 node is also just ignored (wrong unit-address BTW).
I think you're also forgetting the later unflattened parsing of
/reserved-memory. The other complication IIRC is booting with UEFI
does it's own reserved memory table which often uses the DT table as
its source.
Rob
