Hi Stephen,

On Tue, Sep 24, 2019 at 10:41:33PM -0700, Stephen Boyd wrote:

The DT binding could also be simplified somewhat. Currently a path needs
to be specified in DT for each and every use case that is possible for a
device to want. Typically the path is to memory, which looks to be
reserved for in the binding with the "dma-mem" named path, but sometimes
the path is from a device to the CPU or more generically from a device
to another device which could be a CPU, cache, DMA master, or another
device if some sort of DMA to DMA scenario is happening. Let's remove
the pair part of the binding so that we just list out a device's
possible endpoints on the bus or busses that it's connected to.

If the kernel wants to figure out what the path is to memory or the CPU
or a cache or something else it should be able to do that by finding the
node for the "destination" endpoint, extracting that node's
"interconnects" property, and deriving the path in software. For
example, we shouldn't need to write out each use case path by path in DT
for each endpoint node that wants to set a bandwidth to memory. We
should just be able to indicate what endpoint(s) a device sits on based
on the interconnect provider in the system and then walk the various
interconnects to find the path from that source endpoint to the
destination endpoint.

The dma-mem name is used by the OF core to adjust the mapping of the
devices as well. So, any solution needs to be generic (or provide a
generic helper).

Maxime