From mboxrd@z Thu Jan 1 00:00:00 1970 Delivery-date: Wed, 23 Jun 2021 08:15:02 +0200 Received: from metis.ext.pengutronix.de ([2001:67c:670:201:290:27ff:fe1d:cc33]) by lore.white.stw.pengutronix.de with esmtp (Exim 4.92) (envelope-from ) id 1lvwAA-0006HW-O4 for lore@lore.pengutronix.de; Wed, 23 Jun 2021 08:15:02 +0200 Received: from bombadil.infradead.org ([2607:7c80:54:e::133]) by metis.ext.pengutronix.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1lvwA9-0005EV-VA for lore@pengutronix.de; Wed, 23 Jun 2021 08:15:02 +0200 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date: Message-ID:From:References:To:Subject:Reply-To:Cc:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Owner; bh=3db2FcV8Yx7Eer1VHHVZ2guK4hxBTOZXTVXGBksaZN0=; b=fil8OIe7MLqrwx1KwvS+H3e12o lJFIqXXQGjbvD5MrVWMp6BUoplc9BB2CnkijV/5ccxgxTiyIGdNOP9+lvas4I8WmI9ViazL7qCTqu X3SP2vlWVHliv1MJD2Pv7rYbmtq/M7AvInUTNeYYbYV7faNeWP/lyYu/1SeQCMZYo0lAK5sbPAmX5 ueMdcTLEK4N9wIQ7SKaV5IYpWRykwvMtPfxFQVQn6nezFgZ2z0VzT+cZg7pQTktO4gFiYgSwMguFb XIgnAMP47vPBBmt24Fh2BXJxmo829INMUl8BcCuDTzUZGReqVb1ViD6t66CEQ0bLs+a/gUJ4KvhI4 BuskDybg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1lvw8o-009WtI-81; Wed, 23 Jun 2021 06:13:38 +0000 Received: from metis.ext.pengutronix.de ([2001:67c:670:201:290:27ff:fe1d:cc33]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1lvw8i-009Wrb-05 for barebox@lists.infradead.org; Wed, 23 Jun 2021 06:13:33 +0000 Received: from gallifrey.ext.pengutronix.de ([2001:67c:670:201:5054:ff:fe8d:eefb] helo=[127.0.0.1]) by metis.ext.pengutronix.de with esmtp (Exim 4.92) (envelope-from ) id 1lvw8g-00054X-2c; Wed, 23 Jun 2021 08:13:30 +0200 To: Sascha Hauer , Barebox List References: <20210623051632.30253-1-s.hauer@pengutronix.de> <20210623051632.30253-17-s.hauer@pengutronix.de> From: Ahmad Fatoum Message-ID: Date: Wed, 23 Jun 2021 08:13:23 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.2 MIME-Version: 1.0 In-Reply-To: <20210623051632.30253-17-s.hauer@pengutronix.de> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210622_231332_121289_8F6D0EBE X-CRM114-Status: GOOD ( 36.20 ) X-BeenThere: barebox@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "barebox" X-SA-Exim-Connect-IP: 2607:7c80:54:e::133 X-SA-Exim-Mail-From: barebox-bounces+lore=pengutronix.de@lists.infradead.org Subject: Re: [PATCH 16/17] Documentation: Add documentation for device tree overlays X-SA-Exim-Version: 4.2.1 (built Wed, 08 May 2019 21:11:16 +0000) X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); Unknown failure Hi, some bikeshedding incoming. On 23.06.21 07:16, Sascha Hauer wrote: > Document the recently gained device tree overlay features. > > Signed-off-by: Sascha Hauer > --- > Documentation/user/devicetree.rst | 37 +++++++++++++++++++++++++++++++ > 1 file changed, 37 insertions(+) > > diff --git a/Documentation/user/devicetree.rst b/Documentation/user/devicetree.rst > index 4be6a1e703..d78394b7aa 100644 > --- a/Documentation/user/devicetree.rst > +++ b/Documentation/user/devicetree.rst > @@ -75,3 +75,40 @@ It is important to know that these commands normally work on the internal > devicetree. If you want to modify the devicetree the kernel is started with > see the -f options to of_property and of_node. This option will register the > operation for later execution on the Kernel devicetree. > + > +Device tree overlays > +-------------------- > + > +barebox has support for device tree overlays. barebox knows two different trees, > +the live tree and the device tree the kernel is started with. Both can be applied > +overlays to. > + > +Device tree overlays on the live tree > +..................................... > + > +While the live tree can be patched by board code, barebox does not > +detect any changes to the live tree. To let the overlays have any effect, board > +code must make sure the live tree is patched before the devices are instanciated > +from it. > + > +Device tree overlays on the kernel device tree > +.............................................. > + > +Overlays can be applied to the kernel device tree before it is handed over to > +the kernel. The behaviour is controlled by different variables: > + > +``global.of_overlay_dir`` Convention seems to be that attributes of the same thing are preceded by a `.', e.g.: global.of.overlay.dir global.of.overlay.compatible global.of.overlay.filepattern (I think the `.' between of and overlay is not a bad idea, as we may decide to have e.g. global.of.compatible in future) > + Overlays are read from this directory. barebox will try to apply all overlays > + found here if not limited by one of the other variables below. When using > + bootloader spec this variable will be temporarily overwritten with > + ``$mountpoint/overlays`` where ``$mountpoint`` is the path where the filesystem > + containing the bootloader spec entries are located. Couldn't paths be interpreted relative to the $mountpoint? That way you can make overlays the default always and have the user override it if they prefer something else? > +``global.of_overlay_compatible`` > + This is a space separated list of compatibles. Only overlays matching one of > + these compatibles will be applied. When this list is empty then all overlays > + will be applied. Overlays that don't have a compatible are considered being > + always compatible. Makes sense. > +``global.of_overlay_filepattern`` > + This is a space separated list of file patterns. An overlay is only applied > + when its filename matches one of the patterns. The patterns can contain > + ``*`` and ``?`` as wildcards. When empty, all files are applied. Similarly, we could have ``*`` as a default. In future, I think we will want to have $global.of.overlay.filters. Board code can register filters that do more than look into compatibles and file patterns, e.g. compare a property with a value in EEPROM. If a user wants to make use of it, they can add the name of the filter into $global.of.overlay.filters. But this can be retrofitted: The variable will have filepattern and compatible filters as default, so no breakage. Cheers, Ahmad -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox