[BUG] dma-ranges, reserved memory regions, dma_alloc_coherent: possible bug?

[Daniele Alessandrelli <daniele.alessandrelli@gmail.com>]

Hi,

It looks like dma_alloc_coherent() is setting the dma_handle output
parameter to the memory physical address and not the device bus
address when the device is using reserved memory regions for DMA
allocation. This is despite using 'dma_ranges' in the device tree to
describe the DMA memory mapping. Is this expected behavior or a bug?

Here is a reduced version of the device tree I'm using:
\ {
        reserved-memory {
                #address-cells = <2>;
                #size-cells = <2>;
                ranges;
                mydev_rsvd: rsvd_mem@494800000 {
                        compatible = "shared-dma-pool";
                        reg = <0x4 0x94800000 0x0 0x200000>;
                        no-map;
                };
        };
        soc {
                compatible = "simple-bus";
                #address-cells = <2>;
                #size-cells = <2>;
                ranges;
                dma_ranges;

                mybus {
                        ranges = <>;
                        dma-ranges = <>;
                        compatible = "simple-bus";
                        #address-cells = <2>;
                        #size-cells = <2>;
                        ranges =     <0x0 0x0  0x0 0x0  0x0 0x80000000>;
                        dma-ranges = <0x0 0x80000000  0x4 0x80000000
0x0 0x80000000>;

                        mydevice {
                                compatible = "my-compatible-string";
                                memory-region = <&mydev_rsvd>;
                        }
                }
        }
};

It looks like this issue was previously fixed by commit c41f9ea998f3
("drivers: dma-coherent: Account dma_pfn_offset when used with device
tree") which introduced a new function ('dma_get_device_base()') to
return the reserved memory address as seen by the device. However,
such a function, even if still there, is not used anymore in latest
code (as of v5.4-rc2). Was that done for a specific reason? Or is it
just a mistake?

Regards,
Daniele
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