26f47fdd8f
FDT overlays is de-facto standard for describing expansion boards like
Beaglebone capes or Raspberry Pi shields. The ides is to have basic
DTB for base board and overlays DTB for shields/capes and to construct
final DTB either using human-readable configuration or some
self-discovery mechanism. I believe this approach can also be expanded
to support dynamically loadable FPGA bitstreams on systems like
Zedboard/Zybo.
Overlaying process is simmilar to executable link process for
binaries: each DTB has "exported" symbols and "undefined" symbols, the
latter are resolved using information for the former obtained from
base DTB or one of the overlays applied earlier (more rare case).
This symbols information is not generated by standard dtc that FreeBSD
has in base system, patched[1] version required to produces
overlay-compatible blobs. So although DTB files generated by
buildkernel do not support overlays there are enough
vendor/community-provided DTB blobs ciruclating around to justify
committing this change to ubldr.
This commit introduces handler for "fdt_overlays" variable that can be
defined either as a loader env variable or U-Boot env variable.
fdt_overlays is comma-separated list of .dtbo files located in
/boot/dtb/ directory along with base .dtb. ubldr loads files and
applies them one-by-one to base .dtb and then passes result blob to
the kernel.
[1] dd6a0533e8
Differential Revision: https://reviews.freebsd.org/D3180
35 lines
1.5 KiB
C
35 lines
1.5 KiB
C
/*-
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* Copyright (c) 2015 Oleksandr Tymoshenko <gonzo@FreeBSD.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* $FreeBSD$
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*/
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#ifndef FDT_OVERLAY_H
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#define FDT_OVERLAY_H
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int fdt_overlay_apply(void *main_fdtp, void *overlay_fdtp, size_t overlay_length);
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#endif /* FDT_OVERLAY_H */
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