From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D2FCDC433F5 for ; Sat, 5 Feb 2022 02:14:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1356172AbiBECOY (ORCPT ); Fri, 4 Feb 2022 21:14:24 -0500 Received: from mail-oi1-f169.google.com ([209.85.167.169]:40460 "EHLO mail-oi1-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1355924AbiBECOX (ORCPT ); Fri, 4 Feb 2022 21:14:23 -0500 Received: by mail-oi1-f169.google.com with SMTP id q8so10635815oiw.7 for ; Fri, 04 Feb 2022 18:14:23 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=bavDyoeix3ivKrmvk1c86k8fQHTEv2BfyXOQ+LGiGnA=; b=V6Z4xlDwZcHXVwTd1eEEKFKKeJVT0Q6uSyerW6YMVFxhwH77cKU3ETPWnZKyC9NhTd lobJUDWiJDHIbPzl4iMNNReNQ5yPw/nxJvZUkuLbyyUzTnZSLUYrZICGyq4zKKcfD60M rmt7WofVg4SsPeAlNO6MyRcX0A+6K88W4EuoHF5P/PEbPAu5xXZrwtxsNUjq6fBjhOQh CGLXPFy61jLQOiKpBnwfRcZweDcD+99oQ9x8YtyMI/oX0ZIQdTtwGf2lQ6GZ6BIweya6 TqL5y45Z3PmvdMbiBcZ4SMWBdDu4nrIeFhUXPkYUcoYbarKLtuj4M/WRCAJ3m9YWbJUm WCjw== X-Gm-Message-State: AOAM53094tQaVRayD3HVRt9vHJI+/fWB5AZqT0fJJRIS0YjDmhYoKuFy u8oItcDL7ffSMd5zht0WPg== X-Google-Smtp-Source: ABdhPJzohhI86BDByZJvtg/GYgD3FQPT2/j3rlDpD888Vi5x4ag/iD4VE+2Pi/X/ul8DPGRoE3J0Dw== X-Received: by 2002:aca:c056:: with SMTP id q83mr2812199oif.294.1644027263107; Fri, 04 Feb 2022 18:14:23 -0800 (PST) Received: from robh.at.kernel.org (66-90-148-213.dyn.grandenetworks.net. [66.90.148.213]) by smtp.gmail.com with ESMTPSA id i23sm1389213otj.19.2022.02.04.18.14.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Feb 2022 18:14:22 -0800 (PST) Received: (nullmailer pid 3618455 invoked by uid 1000); Sat, 05 Feb 2022 02:14:21 -0000 Date: Fri, 4 Feb 2022 20:14:21 -0600 From: Rob Herring To: Stefano Stabellini Cc: Robin Murphy , Sergiy Kibrik , Julien Grall , Oleksandr Tyshchenko , "devicetree@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "xen-devel@lists.xenproject.org" Subject: Re: [PATCH v3 1/2] dt-bindings: arm: xen: document Xen iommu device Message-ID: References: <20220117123251.140867-1-Sergiy_Kibrik@epam.com> <20220117123251.140867-2-Sergiy_Kibrik@epam.com> <447f89ca-86c0-dc35-e7ac-e6639a573670@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On Wed, Jan 26, 2022 at 10:56:39AM -0800, Stefano Stabellini wrote: > On Wed, 26 Jan 2022, Robin Murphy wrote: > > On 2022-01-26 15:09, Sergiy Kibrik wrote: > > > Hi Robin, > > > > > > > > > > > This could break Linux guests, since depending on the deferred probe > > > > timeout setting it could lead to drivers never probing because the "IOMMU" > > > > never becomes available. > > > > > > > > > > I've noticed no deferred probe timeouts when booting with this patch. Could > > > you please explain more on how this would break guests? > > > > Right now I think it would actually require command-line intervention, e.g. > > "fw_devlink=on" or "deferred_probe_timeout=3600" (with modules enabled for the > > latter to take full effect), but I'm wary of the potential for future config > > options to control those behaviours by default. fw_devlink=on is now the default (for at least a couple of cycles). > > If deferred_probe_timeout=3600 was specified, we would just need an > IOMMU driver in Linux for the "xen,iommu-el2-v1" node to solve the > problem, right? I guess I am trying to say that it wouldn't be a device > tree interface problem but rather a Linux implementation discussion. You would have to add that IOMMU driver to old, existing kernels if you want compatibility with a new DT. Otherwise, that kernel would stop booting with a new DT. Rob