From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932430AbcBHWYa (ORCPT ); Mon, 8 Feb 2016 17:24:30 -0500 Received: from v094114.home.net.pl ([79.96.170.134]:42549 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S932149AbcBHWY2 (ORCPT ); Mon, 8 Feb 2016 17:24:28 -0500 From: "Rafael J. Wysocki" To: Stefano Stabellini Cc: "Rafael J. Wysocki" , Shannon Zhao , "linux-arm-kernel@lists.infradead.org" , ard.biesheuvel@linaro.org, stefano.stabellini@citrix.com, david.vrabel@citrix.com, Catalin Marinas , Will Deacon , Mark Rutland , julien.grall@citrix.com, xen-devel@lists.xen.org, "devicetree@vger.kernel.org" , linux-efi@vger.kernel.org, Linux Kernel Mailing List , ian.campbell@citrix.com, Shannon Zhao , peter.huangpeng@huawei.com, Len Brown , "open list:ACPI" Subject: Re: [PATCH v4 01/17] Xen: ACPI: Hide UART used by Xen Date: Mon, 08 Feb 2016 23:25:37 +0100 Message-ID: <2213954.ztOe55fprN@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/4.5.0-rc1+; KDE/4.11.5; x86_64; ; ) In-Reply-To: References: <1454641552-12576-1-git-send-email-zhaoshenglong@huawei.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Monday, February 08, 2016 10:57:01 AM Stefano Stabellini wrote: > On Sat, 6 Feb 2016, Rafael J. Wysocki wrote: > > On Fri, Feb 5, 2016 at 4:05 AM, Shannon Zhao wrote: > > > From: Shannon Zhao > > > > > > ACPI 6.0 introduces a new table STAO to list the devices which are used > > > by Xen and can't be used by Dom0. On Xen virtual platforms, the physical > > > UART is used by Xen. So here it hides UART from Dom0. > > > > > > Signed-off-by: Shannon Zhao > > > Reviewed-by: Stefano Stabellini > > > > Well, this doesn't look right to me. > > > > We need to find a nicer way to achieve what you want. > > I take that you are talking about how to honor the STAO table in Linux. > Do you have any concrete suggestions? I do. The last hunk of the patch is likely what it needs to be, although I'm not sure if the place it is added to is the right one. That's a minor thing, though. The other part is problematic. Not that as it doesn't work, but because of how it works. With these changes the device will be visible to the OS (in fact to user space even), but will never be "present". I'm not sure if that's what you want? It might be better to add a check to acpi_bus_type_and_status() that will evaluate the "should ignore?" thing and return -ENODEV if this is true. This way the device won't be visible at all. Thanks, Rafael -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.