of_reserved_mem_device_init_by_idx() returns -EINVAL if "memory-region" is missing

[Alexey Brodkin]

Hi Marek,

We used to use of_reserved_mem_device_init() in such a context in GPU drivers:
-------------------->8-------------------
        /* Get the optional framebuffer memory resource */
        ret = of_reserved_mem_device_init(drm->dev);
        if (ret && ret != -ENODEV)
                return ret;
-------------------->8-------------------

The point is we may have a dedicated reserved memory area or may not have 
(depends on a particular .dts).
Our expectation is if reserved memory area is missing then 
of_reserved_mem_device_init()
just returns -ENODEV and it used to work like this.

Now with your commit 59ce4039727e "of: reserved_mem: add support for using 
more than one region for given device"
behavior is different. of_reserved_mem_device_init_by_idx() has this:
-------------------->8-------------------
        target = of_parse_phandle(np, "memory-region", idx);
        if (!target)
                return -EINVAL;
-------------------->8-------------------

So I'm wondering which part should be fixed:
 1) of_reserved_mem itself or
 2) users of of_reserved_mem_device_init()

Any thoughts?

Regards,
Alexey