From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay7-d.mail.gandi.net (relay7-d.mail.gandi.net [217.70.183.200]) (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 4865515ECEC; Fri, 10 May 2024 07:32:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.70.183.200 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715326329; cv=none; b=QYvtOMmNbTY3p+/ggu+//JZXRnWxww+FNu9+Fe32UEZOcncI1OEzJb+Ie3IiDaMltocrFu/LXEmE1JQ2ZLDCFmKQyyBAaMR85yO1B2qGFEtJxc2+U37AonEPhea6dp6NsWfuQSdxHnvIxQM+wuP4nDjt03eAuRiXTvQp6FH+zr8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715326329; c=relaxed/simple; bh=Fckdb3Fian35DrO+vC9ujlpyzWqeeX/x7xTu4QrzFlw=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=PbmYlYIq26JPvYa4PIlrZAm13oVApYn/It3IK3rvk73gY9TP+9SUvjm7aEWLupVfbJ1WtEu7G4ozYQPFKENpKUMKw8QeJ8isfrC3hUIuDGvx8elmmz7hKCywEwUE+u7MFmrrZTqwDiStRXNMxRIXH5f4ikmODBxd5P9x4m1YT38= 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=nuQUwfNq; arc=none smtp.client-ip=217.70.183.200 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="nuQUwfNq" Received: by mail.gandi.net (Postfix) with ESMTPSA id E2D6320008; Fri, 10 May 2024 07:31:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=gm1; t=1715326319; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=gy0lQX70PJvtSy4wE21NBe3LM5+X5IH8D2WT9ewXI5o=; b=nuQUwfNqdtjSjH9txQZFKddvqweW0O0bXvsoAWLS3Gjl4smDIbDR3+Mmx56Pol2mkPjVKc Q5+gZgEuNw6Vu1mThyKSTu4fuISqNrA7oQGaM9dX23bQ2Edr0F/Zd5r35Xm3VUKKy1wMaA ZO+mEd89ImY+2pJOiqHVQo+fCvnAyIPrDVXJ28LZX3WTFz2Zg+HP3MspHMVJLJ4w9mWeAD YzhcWmocPrA275DAB2iq+0X0zIxav0W2wMoVGBXN9LfdG5V8aiYOLmwVp9lQfnleUPnK0e ij5NxkL8Q6m1jF/rrIhtX6RbYvJODmwsZDCQymmrXBcUQlbuRym3g5bXxC91tQ== Date: Fri, 10 May 2024 09:31:56 +0200 From: Luca Ceresoli To: "devicetree@vger.kernel.org" Cc: Krzysztof Kozlowski , Bartosz Golaszewski , Doug Anderson , Chen-Yu Tsai , Matt Coster , Thomas Petazzoni , Alexandre Belloni , Maxime Chevallier , =?UTF-8?Q?Herv=C3=A9?= Codina , Rob Herring , Conor Dooley , Saravana Kannan , linux-kernel@vger.kernel.org Subject: Re: Hotplug hardware with (un)loadable DT overlays - unconference meeting notes Message-ID: <20240510093156.13bfcd34@booty> In-Reply-To: <20240426115141.201f257a@booty> References: <20240426115141.201f257a@booty> Organization: Bootlin X-Mailer: Claws Mail 4.0.0 (GTK+ 3.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-GND-Sasl: luca.ceresoli@bootlin.com Hello, On Fri, 26 Apr 2024 11:51:41 +0200 Luca Ceresoli wrote: [...] > We described 2 use cases we are working on at Bootlin. > > One use case is for the LAN966x, a classic SoC that can be however be > started in "endpoint mode", i.e. with the CPU cores deactivated and a > PCI endpoint that allows an external CPU to access all the peripherals > over PCIe. In practice the whole SoC would be used as a peripheral chip > providing lots of devices for another SoC where the OS runs. This use > case has been described by Rob Herring and Lizhi Hou at LPC 2023 [4][5]. > > The other use case, which was discussed in more detail, is for an > industrial product under development by a Bootlin customer, which is a > regular, self-standing embedded Linux system with a connector allowing > to connect an add-on with additional peripherals. The add-on > peripherals are on I2C, MIPI DSI and potentially other non-discoverable > busses (there are also peripherals on natively hot-pluggable busses > such as USB and Ethernet, but by their nature they don't need special > work). > > For both use cases (and perhaps others we are unaware of) runtime > loading/unloading DT overlays appears as the most fitting technique. > Except it is not yet ready for real usage. > > For it to work, we highlighted 3 main areas in need of work in the > Linux kernel: > > 1. how to describe the connector and the add-ons in device tree > (bindings etc) -- only relevant for the 2nd use case > 2. implementation of DT overlays for adding/removing the add-on > peripherals > 3. fixing issues with various subsystems and drivers that don't react > well on device removal Quick update: I just sent a series with a proposal covering items 1 and 2: https://lore.kernel.org/all/20240510-hotplug-drm-bridge-v2-0-ec32f2c66d56@bootlin.com/ Luca -- Luca Ceresoli, Bootlin Embedded Linux and Kernel engineering https://bootlin.com