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From: Heinrich Schuchardt <xypron.glpk@gmx.de>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	linux-efi@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
	Atish Patra <atishp@atishpatra.org>,
	Heinrich Schuchardt <xypron.glpk@gmx.de>
Subject: [PATCH v2 1/2] docs: admin-guide: fdt and initrd load in EFI stub
Date: Sat,  3 Oct 2020 08:37:24 +0200	[thread overview]
Message-ID: <20201003063725.8698-2-xypron.glpk@gmx.de> (raw)
In-Reply-To: <20201003063725.8698-1-xypron.glpk@gmx.de>

Describe how a device tree and an initial RAM disk can be passed to the EFI
Boot Stub.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
---
v2:
	mention EFI_GENERIC_STUB_INITRD_CMDLINE_LOADER (thx Atish)
---
 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..4965dec48af4 100644
--- 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 partition, 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 using
+  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=" command
+  line parameter if CONFIG_EFI_GENERIC_STUB_INITRD_CMDLINE_LOADER is enabled.
+* 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 parameter.
+
+Passing a device-tree to the EFI Boot Stub
+------------------------------------------
+
+A device-tree can be passed to the EFI Boot Stub in decreasing priority using
+
+* command line option dtb=
+* a UEFI configuration table with GUID b1b621d5-f19c-41a5-830b-d9152c69aae0.
+
+The command line option is only available if CONFIG_EFI_ARMSTUB_DTB_LOADER=y
+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=ttyS0 root=/dev/sda4

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

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

 "dtb=" is processed in the same manner as the "initrd=" option that is
 described above.
+
+This option is only available if CONFIG_EFI_ARMSTUB_DTB_LOADER=y and secure
+boot is disabled.
--
2.28.0


  reply	other threads:[~2020-10-03  6:38 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-03  6:37 [PATCH v2 0/2] docs: admin-guide: EFI Boot Stub Heinrich Schuchardt
2020-10-03  6:37 ` Heinrich Schuchardt [this message]
2020-10-03  7:34   ` [PATCH v2 1/2] docs: admin-guide: fdt and initrd load in EFI stub Atish Patra
2020-10-03  8:28     ` Heinrich Schuchardt
2020-10-03 17:16       ` Atish Patra
2020-10-03  6:37 ` [PATCH v2 2/2] docs: admin-guide: EFI stub to main Linux handoff Heinrich Schuchardt

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