From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtpout-03.galae.net (smtpout-03.galae.net [185.246.85.4]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4F5D678F2B; Wed, 1 Apr 2026 15:11:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.246.85.4 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775056301; cv=none; b=h31/+arm8Mv7QXzi6A0HMGOfiqtPw52m0Hia+vK7tt10xkZqHQwT3w8YTiXmEB/7xjExziMcwsYVQtPkKJe3/sLWe6coleDwiG9UHIewXylJwDGh02xYerMaF/3tT4Ex56NYgkjxpEg/9xYO5RjUB2wlMGGyiuPCu/cNL6QND1k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775056301; c=relaxed/simple; bh=cKIfDOUWbBsrybprOAsGROjGbK4Y84gvaNhqScNZQK4=; h=Mime-Version:Content-Type:Date:Message-Id:From:Subject:Cc:To: References:In-Reply-To; b=lkZk8Ab5JhaqZfMa3sJ2JRjor7u/Q72TQm/jLxxUe4irtOHhbyydAic8PORyXGCWFdUGPp6jlx7pQvW3CqGeIF76kFCXzAolpiEksJKKxML0hqpZtOUlxP0C+mNFs3TAHac8aKICxRf+5C8gsCiEmNs+gIbhGogfDmAyxLJ2UWA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=bootlin.com; spf=pass smtp.mailfrom=bootlin.com; dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com header.b=SDIUN68v; arc=none smtp.client-ip=185.246.85.4 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=bootlin.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=bootlin.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com header.b="SDIUN68v" Received: from smtpout-01.galae.net (smtpout-01.galae.net [212.83.139.233]) by smtpout-03.galae.net (Postfix) with ESMTPS id CB5E14E4288D; Wed, 1 Apr 2026 15:11:37 +0000 (UTC) Received: from mail.galae.net (mail.galae.net [212.83.136.155]) by smtpout-01.galae.net (Postfix) with ESMTPS id A053A602BF; Wed, 1 Apr 2026 15:11:37 +0000 (UTC) Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id 6DF6110450346; Wed, 1 Apr 2026 17:11:35 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=dkim; t=1775056296; h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=jm+DFzw2+IHBIt/jYt2bq8VN/6ByxcD2SYWG6Iwk9Hw=; b=SDIUN68vMgi12KLrofW7DOuZgVXMkdYwtwrAiI+SPJM7SCAXyCE7UIzJgEqErLTATDP8VR 04T2LjLw4q3z+fECo0kZ3Hv4jVzOWqkMZYI9JzaQz5IIFdI+5Unb2+zC+XNjyK6OIhTn9k JGfo6GDXFSsOv+Trag7yH/JaGGhoUDMVu0iF8RahNgU9VZxSGjAw3AeSYRIJMLt++wTx1A d91D96tr9YXD6Rs7dLGan2yDLVQNQfWvpLS9qJy9yaZZHH4WbLbYhXE7vTCbLu7Icqi29V oOCxi0ofALuqltF+YGcjugfIqI++jRT03Sxm4gGkxo16EKdDQTTj8Khw/9ytxQ== Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Wed, 01 Apr 2026 17:11:35 +0200 Message-Id: From: "Luca Ceresoli" Subject: Re: [RFC PATCH 09/15] Introduce structured tag value definition Cc: "Ayush Singh" , "Geert Uytterhoeven" , , , , , "Hui Pu" , "Ian Ray" , "Thomas Petazzoni" To: "Herve Codina" , "David Gibson" , "Rob Herring" , "Krzysztof Kozlowski" , "Conor Dooley" X-Mailer: aerc 0.20.1 References: <20260210173349.636766-1-herve.codina@bootlin.com> <20260210173349.636766-10-herve.codina@bootlin.com> In-Reply-To: <20260210173349.636766-10-herve.codina@bootlin.com> X-Last-TLS-Session-Version: TLSv1.3 On Tue Feb 10, 2026 at 6:33 PM CET, Herve Codina wrote: > The goal of structured tag values is to ease the introduction of new > tags in future releases with the capability for an already existing > release to ignore those structured tags. In order to do that data length > related to the unknown tag needs to be identify. ^ identified > Also a flag is present "Also add a flag" > to tell an old release if this tag can be simply skipped or must lead to > an error. > > Structured tag value is defined on 32bit and is defined as follow: > > Bits | 31 | 30 | 29 28 | 27 0| > ------+----+----------+-------------------+--------+ > Fields| 1 | CAN_SKIP | DATA_LNG_ENCODING | TAG_ID | > ------+----+----------+-------------------+--------+ > > Bit 31 is always set to 1 to identified a structured tag value. ^ identify > Bit 30 (CAN_SKIP) is set to 1 if the tag can be safely ignore when its ^ ignored > TAG_ID value is not a known value (unknown tag). If the CAN_SKIP bit is > set to 0 this tag must not be ignored and an error should be reported > when its TAG_ID value is not a known value (unknown tag). > > Bits 29..28 (DATA_LNG_ENCODING) indicates the length of the data related I think "LEN" is more common than "LNG". > to the tag. Following values are possible: > - 0b00: No data. > The tag is followed by the next tag value. > > - 0b01: 1 cell data > The tag is followed by a 1 cell (u32) data. The next tag is > available after this cell. > > - 0b10: 2 cells data > The tag is followed by a 2 cells (2 * u32) data. The next tag > is available after those two cells. > > - 0b11: Data length encoding > The tag is followed by a cell (u32) indicating the size of the > data. This size is given in bytes. Data are available right > after this cell. > > The next tag is available after the data. Padding is present > after the data in order to have the next tag aligned on 32bits. > This padding is not included in the size of the data. > > Bits 27..0 (TAG_ID) is the tag identifier defining a specific tag. > > Introduce the structured tag values definition and some specific tags > reserved for tests based on this structure definition. > > Signed-off-by: Herve Codina > --- > libfdt/fdt.h | 23 +++++++++++++++++++++++ > 1 file changed, 23 insertions(+) > > diff --git a/libfdt/fdt.h b/libfdt/fdt.h > index a07abfc..2e07599 100644 > --- a/libfdt/fdt.h > +++ b/libfdt/fdt.h > @@ -49,6 +49,7 @@ struct fdt_property { > > #define FDT_MAGIC 0xd00dfeed /* 4: version, 4: total size */ > #define FDT_TAGSIZE sizeof(fdt32_t) > +#define FDT_CELLSIZE sizeof(fdt32_t) > > #define FDT_BEGIN_NODE 0x1 /* Start node: full name */ > #define FDT_END_NODE 0x2 /* End node */ > @@ -57,6 +58,28 @@ struct fdt_property { > #define FDT_NOP 0x4 /* nop */ > #define FDT_END 0x9 > > +/* Tag values flags */ > +#define FDT_TAG_STRUCTURED (1<<31) > +#define FDT_TAG_SKIP_SAFE (1<<30) This is called CAN_SKIP in the commit message and SKIP_SAFE here. Using a consistent name would be better IMO. > +#define FDT_TAG_DATA_MASK (3<<28) > +#define FDT_TAG_DATA_NONE (0<<28) > +#define FDT_TAG_DATA_1CELL (1<<28) > +#define FDT_TAG_DATA_2CELLS (2<<28) > +#define FDT_TAG_DATA_LNG (3<<28) I find _LNG (or _LEN) misleading: this is not the length, but rather an enum value telling you the length is stored in the next cell. What about FDT_TAG_DATA_VARLEN? Otherwise looks good. Luca -- Luca Ceresoli, Bootlin Embedded Linux and Kernel engineering https://bootlin.com