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[209.132.180.67]) by mx.google.com with ESMTP id g35-v6si8354571plb.108.2018.09.07.03.44.33; Fri, 07 Sep 2018 03:44:49 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@linaro.org header.s=google header.b=dsfV7mIL; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linaro.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728658AbeIGPXs (ORCPT + 99 others); Fri, 7 Sep 2018 11:23:48 -0400 Received: from mail-it0-f66.google.com ([209.85.214.66]:33475 "EHLO mail-it0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727785AbeIGPXs (ORCPT ); Fri, 7 Sep 2018 11:23:48 -0400 Received: by mail-it0-f66.google.com with SMTP id j198-v6so22507599ita.0 for ; Fri, 07 Sep 2018 03:43:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=HIm926GvTLNI1YtEYht5Y2Bhr82Sga1WnTWGIac+3t8=; b=dsfV7mILJkG1WWiCS+AlUAaH7YkTNwndEsue3FcAk3P2yvcBGKNp5gbqJPPpVbsseM o4X5s4kBvwsPPhaGIPBwSioeT4kHNdWteoMoJtOwD+lMAcOrQCT//BBFOstiTrGjDsZI /bAbedBoXgt7i9FEnZT8Dw2bDbgbPG+IFcxFI= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=HIm926GvTLNI1YtEYht5Y2Bhr82Sga1WnTWGIac+3t8=; b=TH3yVHsJ7x7NB473+ZMJm1si7Q95mznhToMiJWnjuKKWvqAg7QtsEEl3sgACHP5Fpw Nk38BKaLQNKt3OsouGeX/C7XMitVftxvjUFjS5DEPE5uGXQWF35kfM8ORLgLw+jgOeBk D1SIbt4WyQkHlyOWdZZo08khSNMGJnM4EYcIcFfFU2+vPL5lFh4DvHShDSdGtyIsMI1L cgOaLvW7ME37jyThrnRuR3pCNTivrga3sl0V/FuHVuSdpokREx+TtSNTeJkeQphthbIO pEMEVvaIEKgwjE/bzYwJeQWji4dss94mN+3trc5n6rWp1UJxBnnxw9M8Bk6/VbHJp1vr jg2A== X-Gm-Message-State: APzg51CB7GIWJD+gOLQ0ZkRx/YPTLSDPrPapUsYJeKtQwmny0xdOirnB k67HK+kyUdCm/DZvcCwyShS4W6DxgtGz4Hwd114CkQ== X-Received: by 2002:a02:1515:: with SMTP id j21-v6mr6203117jad.2.1536317005902; Fri, 07 Sep 2018 03:43:25 -0700 (PDT) MIME-Version: 1.0 Received: by 2002:a6b:1c06:0:0:0:0:0 with HTTP; Fri, 7 Sep 2018 03:43:25 -0700 (PDT) In-Reply-To: <20180906182927.22318-1-grant.likely@arm.com> References: <20180906182927.22318-1-grant.likely@arm.com> From: Ard Biesheuvel Date: Fri, 7 Sep 2018 12:43:25 +0200 Message-ID: Subject: Re: [PATCH RESEND] efi_stub: update documentation on dtb= parameter To: Grant Likely Cc: linux-efi , Linux Kernel Mailing List , linux-arm-kernel , Olof Johansson , Scott Branden , Catalin Marinas , Will Deacon , Arnd Bergmann , Leif Lindholm , Alexander Graf , nd , Jonathan Corbet Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6 September 2018 at 20:29, Grant Likely wrote: > 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 > Reviewed-by: Alexander Graf > Acked-by: Leif Lindholm > Acked-by: Olof Johansson > Cc: Ard Biesheuvel > Cc: Jonathan Corbet Acked-by: Ard Biesheuvel > --- > > 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 >