[PATCH 0/9] Dynamic DT device nodes

Greg Kroah-Hartman gregkh at linuxfoundation.org
Thu Oct 7 21:31:39 AEDT 2021

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


greg k-h

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