Re: [PATCH v9 02/10] of: reserved_mem: Introduce "ll-map" property

On Thu, Sep 03, 2026 at 11:03:12AM +0100, Vincent Donnefort wrote:

On Wed, Sep 02, 2026 at 12:24:36PM -0500, Rob Herring wrote:

quoted

On Wed, Sep 02, 2026 at 11:47:04AM +0100, Vincent Donnefort wrote:

quoted

Keeping last-level mappings is interesting on some architectures as it
allows mapping/unmapping pages from the kernel direct map without the
risk of splitting blocks which, under the break-before-make rule, may
trigger page-faults the kernel can't handle.

Add an "ll-map" property for reserved-memory regions. When set, it
splits the underlying memblock and sets the MEMBLOCK_LLMAP flag.

Where is this documented? Any DT property must have a schema.

Ack.

quoted

Though I'm not thrilled about more flag properties. Handling all the 
combinations of properties has proven to be painful. Can this be implied 
from the compatible string instead?

Rob

We need this before the kernel direct map has been created (paging_init()).

I would have moved that directly into the driver lend_pool.c, but then it is
probed too late (unflatten_device_tree()).

Any of the node_*() callbacks from struct reserved_mem_ops get called
prior to paging_init(), so these could be used to manually set the
memblock flags in the corresponding drivers.

Thierry