From: Grant Likely <grant.likely@arm.com>
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 <grant.likely@arm.com>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Jonathan Corbet <corbet@lwn.net>
Subject: [PATCH RESEND] efi_stub: update documentation on dtb= parameter
Date: Thu, 6 Sep 2018 19:29:27 +0100 [thread overview]
Message-ID: <20180906182927.22318-1-grant.likely@arm.com> (raw)
The dtb= parameter is no longer the primary mechanism for providing a
devicetree to the kernel. 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 <grant.likely@arm.com>
Reviewed-by: Alexander Graf <agraf@suse.de>
Acked-by: Leif Lindholm <leif.lindholm@linaro.org>
Acked-by: Olof Johansson <olof@lixom.net>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jonathan Corbet <corbet@lwn.net>
---
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
next reply other threads:[~2018-09-06 18:30 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-06 18:29 Grant Likely [this message]
2018-09-07 10:43 ` Ard Biesheuvel
2018-09-09 20:47 ` Jonathan Corbet
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