Re: [PATCH] remoteproc: core: Honor device tree /alias entries when assigning IDs

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On 8/22/23 3:12 PM, Nishanth Menon wrote:
On 13:25-20230822, Mathieu Poirier wrote:
Hi Nishanth,

On Mon, Aug 07, 2023 at 09:02:47AM -0500, Nishanth Menon wrote:
On many platforms, such as Beaglebone-AI64 with many remote
processors, firmware configurations provided by the distributions can
vary substantially depending on the distribution build's functionality
and the specific remote cores enabled in that variant. Ensuring
consistent udev rules mapping remoteproc nodes to constant remote
proc device indices across distributions (yocto, ubuntu, debian and
it's variants, ...) on a board basis can be challenging due to the
various functions of these distributions. Varied device node paths
create challenges for applications that operate on remote processors,
especially in minimal embedded systems(initrd like) that may not
have udev-like capabilities and rely on a more straightforward bare
filesystem. This challenge is similar to that faced by I2C, RTC or the
GPIO subsystems.

I'm puzzled by this patch.  I can see how using an alias can help in boards with
various HW configuration.  That said, and as written above, FW files for remote
processors can vary based on the build's functionality.  As such "remoteproc3"
will reference the same HW device on all distributions but the functionality
enacted by the FW may be different.  As such I don't see how an alias can help
here.  Can you provide a concrete example that highlights the benefits?

Correct - *if* remoteproc3 is the constant node reference.

To take a trivial example: We ran into this issue with:

remoteproc18 apparently changed numbering in a different build.

If remoteproc18 remained the same between different distro builds that
would have probably kept the userspace constant. but it does'nt. it
dependent purely on probe order, which does'nt let userspace remain

Same reason and motivation to do the following:
in one technique to do it - but that only works if all the distros
follow the same udev rules - and there is no reasonable way to enforce
that across distributions.

Enforcing distros to behave the same isn't the job of Device Tree, udev
rules seems like a reasonable place. Anyone dealing with Linux should know
they should not rely on kernel provided device names/numbers
(like with disks, network interfaces, etc.).

If you want to have a path that will always work you could use:


for the same. I don't like that it makes an ABI out of node names,
but better than putting any more Linux configuration in DT IMHO.


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