Re: [PATCH 01/11] of: reserved_mem: fix region count for nodes with multiple reg entries

[Wandun]

在 2026/5/6 09:47, Rob Herring 写道:
> On Wed, Apr 29, 2026 at 02:58:21PM +0800, Chen Wandun wrote:
> > When a reserved-memory node contains multiple reg entries (e.g.,
> > reg = <base1 size1>, <base2 size2>), the count used for
> > total_reserved_mem_cnt is wrong in two places:
> >
> > 1) __reserved_mem_reserve_reg() returns 0 on success regardless of how
> >     many regions it reserved in memblock. The caller in
> >     fdt_scan_reserved_mem() then increments count by just 1.
> Just to make sure, more than 1 worked before the referenced commits? It
> would be easier to just define we only expect/support 1 entry.
Looking at the pre-8a6e02d0c00e code, __reserved_mem_reserve_reg()
reserved memblock memory for all reg entries, but only called
fdt_reserved_mem_save_node() for the first one (guarded by an 'if 
(first)' flag).

So multiple reg entries were never fully supported: subsequent entries
got their memory reserved in memblock, but their metadata was lost
and driver-specific init callbacks were never invoked for them.

The referenced commits made this worse by also breaking the count
tracking, but the root limitation predates them.

I support documenting "only 1 entry supported" based on the
following reasons:

  - of_reserved_mem_lookup() does a name-based linear scan and returns
    the *first* matching entry. A node with N reg entries would create
    N entries with identical names; entries [1..N-1] are permanently
    unreachable via lookup.

  - Drivers like CMA and DMA coherent are designed to initialize a
    single contiguous pool per node_init call. Calling node_init
    multiple times with the same FDT node is not a supported usage.


> > 2) fdt_scan_reserved_mem_late() uses of_flat_dt_get_addr_size() which
> >     only reads the first reg entry. Subsequent entries are never
> >     initialized via fdt_init_reserved_mem_node(), so their metadata is
> >     lost.
> >
> > Fix both issues:
> >   - Make __reserved_mem_reserve_reg() return the actual number of
> >     regions successfully reserved. Update the caller to accumulate
> >     the returned count.
> >   - Rewrite fdt_scan_reserved_mem_late() to use
> >     of_flat_dt_get_addr_size_prop() and iterate all reg entries,
> >     initializing each one via fdt_init_reserved_mem_node().
> >
> > Fixes: 8a6e02d0c00e ("of: reserved_mem: Restructure how the reserved memory regions are processed")
> > Fixes: 00c9a452a235 ("of: reserved_mem: Add code to dynamically allocate reserved_mem array")