On Thu, Oct 7, 2021 at 3:10 AM Zev Weiss <zev@xxxxxxxxxxxxxxxxx> 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? Why can't device tree overlays be used? > To provide that > ability, this series adds support for a new common device-tree > property, a boolean "dynamic" that indicates that the device may come > and go at runtime. When present on a node, the sysfs file for that > node's "status" property is made writable, allowing userspace to do > things like: > > $ echo okay > /sys/firmware/devicetree/.../status > $ echo reserved > /sys/firmware/devicetree/.../status > > to activate and deactivate a dynamic device. > > Because it leans on the OF_DYNAMIC machinery internally, this > functionality will only work on busses that register for OF reconfig > notifications and handle them appropriately (presently platform, i2c, > and spi). This series does not attempt to solve the "dynamic devices > further down the tree" problem [2]; my hope is that handling for OF > reconfig notifications can be extended to other families of devices > (e.g. individual MTD spi-nor flash chips) in the future. What about ACPI and software nodes? How will all this affect the host? > [0] https://lore.kernel.org/openbmc/20210929115409.21254-1-zev@xxxxxxxxxxxxxxxxx/ > [1] https://lore.kernel.org/openbmc/CAL_JsqJH+b5oFuSP+KBLBsN5QTA6xASuqXJWXUaDkHhugXPpnQ@xxxxxxxxxxxxxx/ > [2] https://lore.kernel.org/openbmc/20210929220038.GS17315@packtop/ > [3] https://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git/commit/?id=6663ae07d995f5fbe2988a19858b2f87e68cf929 -- With Best Regards, Andy Shevchenko
