[PATCH 0/9] Dynamic DT device nodes

[Zev Weiss]

On Thu, Oct 07, 2021 at 03:31:39AM PDT, Greg Kroah-Hartman wrote:
>On Thu, Oct 07, 2021 at 02:05:41AM -0700, Zev Weiss wrote:
>> On Thu, Oct 07, 2021 at 12:04:41AM PDT, Andy Shevchenko wrote:
>> > On Thu, Oct 7, 2021 at 3:10 AM Zev Weiss <zev at bewilderbeest.net> wrote:
>> > > This patch series is in some ways kind of a v2 for the "Dynamic
>> > > aspeed-smc flash chips via 'reserved' DT status" series I posted
>> > > previously [0], but takes a fairly different approach suggested by Rob
>> > > Herring [1] and doesn't actually touch the aspeed-smc driver or
>> > > anything in the MTD subsystem, so I haven't marked it as such.
>> > >
>> > > To recap a bit of the context from that series, in OpenBMC there's a
>> > > need for certain devices (described by device-tree nodes) to be able
>> > > to be attached and detached at runtime (for example the SPI flash for
>> > > the host's firmware, which is shared between the BMC and the host but
>> > > can only be accessed by one or the other at a time).
>> >
>> > This seems quite dangerous. Why do you need that?
>>
>> Sometimes the host needs access to the flash (it's the host's firmware,
>> after all), sometimes the BMC needs access to it (e.g. to perform an
>> out-of-band update to the host's firmware).  To achieve the latter, the
>> flash needs to be attached to the BMC, but that requires some careful
>> coordination with the host to arbitrate which one actually has access to it
>> (that coordination is handled by userspace, which then tells the kernel
>> explicitly when the flash should be attached and detached).
>>
>> What seems dangerous?
>>
>> > Why can't device tree overlays be used?
>>
>> I'm hoping to stay closer to mainline.  The OpenBMC kernel has a documented
>> policy strongly encouraging upstream-first development:
>> https://github.com/openbmc/docs/blob/master/kernel-development.md
>>
>> I doubt Joel (the OpenBMC kernel maintainer) would be eager to start
>> carrying the DT overlay patches; I'd likewise strongly prefer to avoid
>> carrying them myself as additional downstream patches.  Hence the attempt at
>> getting a solution to the problem upstream.
>
>Then why not work to get device tree overlays to be merged properly?
>Don't work on a half-of-a-solution when the real solution is already
>here.
>

I had been under the impression that the overlay patches had very dim 
prospects of ever being accepted and that this might be a more tractable 
alternative, but apparently was mistaken -- I'll look into what the 
outstanding issues were with that and perhaps take a stab at addressing 
them.


Zev