From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [PATCH v3 07/24] xen/arm: Introduce xen, passthrough property Date: Mon, 23 Feb 2015 15:43:53 +0000 Message-ID: <54EB4AB9.3030101@linaro.org> References: <1421159133-31526-1-git-send-email-julien.grall@linaro.org> <1421159133-31526-8-git-send-email-julien.grall@linaro.org> <1424446687.30924.311.camel@citrix.com> <54E7686C.9060008@linaro.org> <1424704362.27930.149.camel@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta3.messagelabs.com ([195.245.230.39]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1YPvBH-0004Ni-N9 for xen-devel@lists.xenproject.org; Mon, 23 Feb 2015 15:44:23 +0000 Received: by mail-wi0-f180.google.com with SMTP id h11so18217575wiw.1 for ; Mon, 23 Feb 2015 07:44:21 -0800 (PST) In-Reply-To: <1424704362.27930.149.camel@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Campbell Cc: xen-devel@lists.xenproject.org, tim@xen.org, stefano.stabellini@citrix.com List-Id: xen-devel@lists.xenproject.org Hi Ian, On 23/02/15 15:12, Ian Campbell wrote: > On Fri, 2015-02-20 at 17:01 +0000, Julien Grall wrote: >>>> diff --git a/docs/misc/arm/device-tree/passthrough.txt b/docs/misc/arm/device-tree/passthrough.txt >>>> new file mode 100644 >>>> index 0000000..04645b3 >>>> --- /dev/null >>>> +++ b/docs/misc/arm/device-tree/passthrough.txt >>>> @@ -0,0 +1,7 @@ >>>> +Device passthrough >>>> +=================== >>>> + >>>> +Any device that will be passthrough to a guest should have a property >>>> +"xen,passthrough" in their device tree node. >>>> + >>>> +The device won't be exposed to DOM0 and therefore no driver will be loaded. >>> >>> This (and the commit message to some extent) seem stricter than what I >>> think is actually required here. >>> >>> I understand that it is a very good idea for any sort of passthrough to >>> prevent dom0 from messing with a device before it gets assigned to the >>> eventual guest domain. >>> >>> But AIUI it is not strictly speaking a hard requirement that dom0 does >>> not do this and depending on the device it may be perfectly acceptable >>> for dom0 to drive a device for a bit and then give it to a guest and >>> then have it back again etc. >> >> When the device has the property "xen,passthrough", Xen won't map the >> MMIO and IRQ to DOM0. So it's an hard requirement. > > That's not what I meant. > > What I was getting at is that it's not 100% mandatory for a device you > want to pass through to have the "xen,passthrough" property at all, but > the wording of the binding implies otherwise.. > > There will be at least some devices in the world (even if only trivial > ones) where you can pass them through even if dom0 has been touching > them before. Or dom0 might choose to implement a reset helper for some > device or other. Hmmm right... I will update the binding. Regards, -- Julien Grall