From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail02.groups.io (mail02.groups.io [66.175.222.108]) by spool.mail.gandi.net (Postfix) with ESMTPS id 3F25E740040 for ; Thu, 26 Oct 2023 14:46:57 +0000 (UTC) DKIM-Signature: a=rsa-sha256; bh=TODRvSbSd8Geic1iN5U6722JcCfojYm0ohzrgthNSpU=; c=relaxed/simple; d=groups.io; h=Message-ID:Date:MIME-Version:User-Agent:Subject:To:Cc:References:From:In-Reply-To:Precedence:List-Subscribe:List-Help:Sender:List-Id:Mailing-List:Delivered-To:Reply-To:List-Unsubscribe-Post:List-Unsubscribe:Content-Language:Content-Type:Content-Transfer-Encoding; s=20140610; t=1698331615; v=1; b=rB1TL+DyU1Tw+Mv+uoHy4f6XXHoVwuEBJJUTbgslrbuqW19HzogMBmIO1yEGDmyooK6naB7y t2EEN1ZfG6pFzR2W9p3kvY8sRMtbTUyVlnBupD394B47RMnqKZZmBUYPDIHXmlNNut0y4B6il1P Te+QI8AVosvO8pDjFNQIoZiU= X-Received: by 127.0.0.2 with SMTP id NVtNYY7687511xZBTVbiuaUY; Thu, 26 Oct 2023 07:46:55 -0700 X-Received: from mail.xenproject.org (mail.xenproject.org [104.130.215.37]) by mx.groups.io with SMTP id smtpd.web11.72763.1698331615026197653 for ; Thu, 26 Oct 2023 07:46:55 -0700 X-Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1qw1dN-0005zf-TN; Thu, 26 Oct 2023 14:46:53 +0000 X-Received: from 54-240-197-238.amazon.com ([54.240.197.238] helo=[192.168.13.109]) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1qw1dN-0003jm-J6; Thu, 26 Oct 2023 14:46:53 +0000 Message-ID: <52ab22e6-94c5-4a79-a6f5-2a5c1ed62c27@xen.org> Date: Thu, 26 Oct 2023 15:46:51 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [edk2-devel] [PATCH 0/9] ArmVirtPkg: support two PL011 UARTs To: Peter Maydell , Laszlo Ersek Cc: devel@edk2.groups.io, ardb@kernel.org, Ard Biesheuvel , Gerd Hoffmann , Leif Lindholm , Sami Mujawar References: <20231008153912.175941-1-lersek@redhat.com> <35314dd9-3705-d322-4137-f4708d420e3e@redhat.com> From: "Julien Grall" In-Reply-To: Precedence: Bulk List-Subscribe: List-Help: Sender: devel@edk2.groups.io List-Id: Mailing-List: list devel@edk2.groups.io; contact devel+owner@edk2.groups.io Reply-To: devel@edk2.groups.io,julien@xen.org List-Unsubscribe-Post: List-Unsubscribe=One-Click List-Unsubscribe: X-Gm-Message-State: HGq9NM4B7ta93Na1A1qPwKpmx7686176AA= Content-Language: en-GB Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable X-GND-Status: LEGIT Authentication-Results: spool.mail.gandi.net; dkim=pass header.d=groups.io header.s=20140610 header.b=rB1TL+Dy; dmarc=none; spf=pass (spool.mail.gandi.net: domain of bounce@groups.io designates 66.175.222.108 as permitted sender) smtp.mailfrom=bounce@groups.io Hi, On 26/10/2023 15:21, Peter Maydell wrote: > On Tue, 10 Oct 2023 at 16:33, Laszlo Ersek wrote: >> On 10/10/23 09:43, Ard Biesheuvel wrote: >>> Thanks for looking into this - a cleanup was overdue here. >>> >>> I will take a look in more detail later, but one thing that occurred >>> to me when reading this overview is that having a separate DEBUG >>> serial port would permit us to >>> >>> a) remove it from the DT >> >> ... as in, hide it from Linux, I assume? >> >>> b) add a runtime mapping for it >>> c) keep using it after ExitBootServices >>> >>> This could be useful for debugging issues with the variable store etc. >>> >>> Not saying this is something to address in this series, but I'd like >>> to hear your take on this. >>> >> >> Sounds like a useful feature. >> >> I see four challenges: >> >> >> (1) We'd have to coordinate it with Peter. If we hide any one of the >> serial ports from Linux, that may not be what QEMU intends for Linux to >> happen. Linux currently ties getties to all serial ports -- via the >> serial* aliases, IIUC. Thus, some "positive identification" in the DT >> could be necessary (i.e., that edk2 was welcome to hide that port from >> Linux). >=20 > The potential awkwardness here is that what the guest thinks about > the serial ports depends on the ACPI table fragments which QEMU > provides. EDK2 would need to edit the table fragment to remove any > mention of the second UART if it wanted to hide it from the kernel. > I don't know how hard that would be in EDK2. I am not sure if it would help EDK2 in this case. But we had a similar=20 problem when adding support for ACPI in Xen. It was not trivial to=20 remove the UART from the ACPI tables provided by the host. So we ended=20 up to introduce the STAO table [1]. This is used to describe which=20 device will be hidden to the OS. Cheers, [1] https://wiki.xenproject.org/images/0/02/Status-override-table.pdf --=20 Julien Grall -=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#110107): https://edk2.groups.io/g/devel/message/110107 Mute This Topic: https://groups.io/mt/101834880/7686176 Group Owner: devel+owner@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [rebecca@openfw.io] -=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-