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From:   Heinrich Schuchardt <xypron.glpk@gmx.de>
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     Jonathan Corbet <corbet@lwn.net>, linux-efi@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        =?UTF-8?q?Fran=C3=A7ois=20Ozog?= <francois.ozog@linaro.org>,
        Ilias Apalodimas <ilias.apalodimas@linaro.org>,
        Heinrich Schuchardt <xypron.glpk@gmx.de>
Subject: [PATCH 1/1] docs: admin-guide: fdt and initrd load in EFI stub
Date:   Fri,  2 Oct 2020 19:11:12 +0200
Message-Id: <20201002171112.22738-1-xypron.glpk@gmx.de>
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Describe how a device tree and an initial RAM disk can be passed to the EF=
I
Boot Stub.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
=2D--
 Documentation/admin-guide/efi-stub.rst | 35 ++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/Documentation/admin-guide/efi-stub.rst b/Documentation/admin-=
guide/efi-stub.rst
index 833edb0d0bc4..86f50a33884c 100644
=2D-- a/Documentation/admin-guide/efi-stub.rst
+++ b/Documentation/admin-guide/efi-stub.rst
@@ -38,6 +38,34 @@ arch/arm/boot/zImage should be copied to the system par=
tition, and it
 may not need to be renamed. Similarly for arm64, arch/arm64/boot/Image
 should be copied but not necessarily renamed.

+Passing an initial RAM disk to the EFI Boot Stub
+------------------------------------------------
+
+The following means sorted by decreasing priority can be used to provide =
an
+initial RAM disk to the EFI Boot Stub:
+
+* The firmware may provide a UEFI Load File 2 Protocol. The stub will try=
 to
+  load the RAM disk by calling the LoadFile() service of the protocol usi=
ng
+  a vendor device path with the vendor GUID
+  5568e427-0x68fc-4f3d-ac74-ca555231cc68.
+* Next the EFI stub will try to load the file indicated by the "initrd=3D=
" command
+  line parameter.
+* The prior boot stage may pass the location of the initial RAM disk via =
the
+  "linux,initrd-start" and "linux,initrd-end" properties of the "/chosen"=
 node
+  of the device-tree.
+
+The first two items are inhibited by the "noinitrd" command line paramete=
r.
+
+Passing a device-tree to the EFI Boot Stub
+------------------------------------------
+
+A device-tree can be passed to the EFI Boot Stub in decreasing priority u=
sing
+
+* command line option dtb=3D
+* a UEFI configuration table with GUID b1b621d5-f19c-41a5-830b-d9152c69aa=
e0.
+
+The command line option is only available if CONFIG_EFI_ARMSTUB_DTB_LOADE=
R=3Dy
+and secure boot is disabled.

 Passing kernel parameters from the EFI shell
 --------------------------------------------
@@ -46,6 +74,10 @@ Arguments to the kernel can be passed after bzImage.efi=
, e.g.::

 	fs0:> bzImage.efi console=3DttyS0 root=3D/dev/sda4

+The "noinitrd" option
+---------------------
+
+The "noinitrd" option stops the EFI stub from loading an initial RAM disk=
.

 The "initrd=3D" option
 --------------------
@@ -98,3 +130,6 @@ CONFIGURATION TABLE.

 "dtb=3D" is processed in the same manner as the "initrd=3D" option that i=
s
 described above.
+
+This option is only available if CONFIG_EFI_ARMSTUB_DTB_LOADER=3Dy and se=
cure
+boot is disabled.
=2D-
2.28.0