Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966685Ab3DRIvW (ORCPT ); Thu, 18 Apr 2013 04:51:22 -0400 Received: from cantor2.suse.de ([195.135.220.15]:38812 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965897Ab3DRIvT convert rfc822-to-8bit (ORCPT ); Thu, 18 Apr 2013 04:51:19 -0400 References: <1366264344-28025-1-git-send-email-pranavkumar@linaro.org> Mime-Version: 1.0 (1.0) In-Reply-To: Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8BIT Message-Id: <7C17A12D-F7C5-48ED-8D2F-22D8A7F289E3@suse.de> Cc: Marc Zyngier , "linaro-kernel@lists.linaro.org" , "patches@linaro.org" , "linux-kernel@vger.kernel.org" , "kvmarm@lists.cs.columbia.edu" , "linux-arm-kernel@lists.infradead.org" X-Mailer: iPhone Mail (10B142) From: Alexander Graf Subject: Re: [RFC] arm64: Early printk support for virtio-mmio console devices. Date: Thu, 18 Apr 2013 10:51:14 +0200 To: Peter Maydell Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1492 Lines: 33 Am 18.04.2013 um 10:30 schrieb Peter Maydell : > On 18 April 2013 07:49, Marc Zyngier wrote: >> If you need an early console, why not simply wire the 8250 emulation in >> kvmtool to be useable from the MMIO bus? I reckon this would solve your >> problem in a more elegant way... > > The other approach I thought of would be something involving > defining a hypercall interface for console I/O, in the same > way that we have hypercalls for "start cpu"/"stop cpu"/etc. > Is there any mileage in considering that approach, or is it > a non-starter? It's exactly what we had for the s390-virtio machine. Virtio-console as console device plus a hypercall for early printk. It was a mess. Trying to inject character output that lands in machine context, where hypercalls get handled, inside of a specific virtio-console device, which owns the char output, is hard. We haven't found any good solution in qemu to layer this properly. The closest approach to something workable was to create 2 char outputs and mux them together, like you usually would mus monitor and serial. Good luck muxing that one again with the monitor :). I'd rather spare you guys from going through the same pain. Alex -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/