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Thu, 6 Sep 2018 18:30:08 +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, nd@arm.com, Grant Likely , Ard Biesheuvel , Jonathan Corbet Subject: [PATCH RESEND] efi_stub: update documentation on dtb= parameter Date: Thu, 6 Sep 2018 19:29:27 +0100 Message-Id: <20180906182927.22318-1-grant.likely@arm.com> X-Mailer: git-send-email 2.11.0 MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [217.43.126.139] X-ClientProxiedBy: DB7PR04CA0010.eurprd04.prod.outlook.com (2603:10a6:10:12::23) To VI1PR0801MB1759.eurprd08.prod.outlook.com (2603:10a6:800:5b::8) X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 0a391ed3-409f-4012-9f1b-08d61426c6a1 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:VI1PR0801MB1759; 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Now either firmware or the boot selector (ex. Grub) should provide the devicetree and dtb= 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 Reviewed-by: Alexander Graf Acked-by: Leif Lindholm Acked-by: Olof Johansson Cc: Ard Biesheuvel Cc: Jonathan Corbet --- Resending because original post included Arm corporate disclaimer. 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=" 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=" command line option, -and is processed in the same manner as the "initrd=" 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=" 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= is used to override +the device tree, then any runtime data provided by firmware will be +lost. The dtb= 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=" is processed in the same manner as the "initrd=" option that is described above. -- 2.11.0