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Wed, 5 Sep 2018 19:08:22 +0000 From: Grant Likely To: linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Cc: olof@lixom.net, scott.branden@broadcom.com, catalin.marinas@arm.com, will.deacon@arm.com, arnd@arndb.de, leif.lindholm@linaro.org, agraf@suse.de, Grant Likely , Ard Biesheuvel , Jonathan Corbet Subject: [PATCH] efi_stub: update documentation on dtb= parameter Date: Wed, 5 Sep 2018 20:07:50 +0100 Message-Id: <20180905190750.4566-1-grant.likely@arm.com> X-Mailer: git-send-email 2.11.0 MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [217.140.96.140] X-ClientProxiedBy: AM5PR04CA0001.eurprd04.prod.outlook.com (2603:10a6:206:1::14) To AM5PR0801MB1746.eurprd08.prod.outlook.com (2603:10a6:203:3b::12) X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 0370c700-a457-43cc-87bf-08d61362f340 X-MS-Office365-Filtering-HT: Tenant X-Microsoft-Antispam: BCL:0;PCL:0;RULEID:(7020095)(4652040)(8989137)(4534165)(4627221)(201703031133081)(201702281549075)(8990107)(5600074)(711020)(4618075)(2017052603328)(7153060)(7193020);SRVR:AM5PR0801MB1746; 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Now either firmware or the boot selector (ex. Grub) should provide the devicetree and dtb=3D should only be used for debug or when using firmware that doesn't understand DT. Update the EFI stub documentation to reflect the current usage. Signed-off-by: Grant Likely Cc: Ard Biesheuvel Cc: Jonathan Corbet --- Documentation/efi-stub.txt | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) diff --git a/Documentation/efi-stub.txt b/Documentation/efi-stub.txt index 41df801f9a50..833edb0d0bc4 100644 --- a/Documentation/efi-stub.txt +++ b/Documentation/efi-stub.txt @@ -83,7 +83,18 @@ is passed to bzImage.efi. The "dtb=3D" option ----------------- -For the ARM and arm64 architectures, we also need to be able to provide a -device tree to the kernel. This is done with the "dtb=3D" command line opt= ion, -and is processed in the same manner as the "initrd=3D" option that is +For the ARM and arm64 architectures, a device tree must be provided to +the kernel. Normally firmware shall supply the device tree via the +EFI CONFIGURATION TABLE. However, the "dtb=3D" command line option can +be used to override the firmware supplied device tree, or to supply +one when firmware is unable to. + +Please note: Firmware adds runtime configuration information to the +device tree before booting the kernel. If dtb=3D is used to override +the device tree, then any runtime data provided by firmware will be +lost. The dtb=3D option should only be used either as a debug tool, or +as a last resort when a device tree is not provided in the EFI +CONFIGURATION TABLE. + +"dtb=3D" is processed in the same manner as the "initrd=3D" option that is described above. -- 2.11.0 IMPORTANT NOTICE: The contents of this email and any attachments are confid= ential and may also be privileged. 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