On Fri, Jul 23, 2021 at 3:40 PM Atish Patra [off-list ref] wrote:

Currently, linux,dma-default is used to reserve a global non-coherent pool
to allocate memory for dma operations. This can be useful for RISC-V as
well as the ISA specification doesn't specify a method to modify PMA
attributes or page table entries to define non-cacheable area yet.
A non-cacheable memory window is an alternate options for vendors to
support non-coherent devices. "dma-ranges" must be used in conjunction with
"linux,dma-default" property to define one or more mappings between device
and cpu accesible memory regions.

'dma-ranges' applies to buses. And, well, maybe devices when the bus
is not well defined. It is not a reserved-memory property.

Rob

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