Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753053Ab3DZLTx (ORCPT ); Fri, 26 Apr 2013 07:19:53 -0400 Received: from cantor2.suse.de ([195.135.220.15]:48350 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751995Ab3DZLTw convert rfc822-to-8bit (ORCPT ); Fri, 26 Apr 2013 07:19:52 -0400 Subject: Re: [PATCH 0/2] Early printk support for virtio console devices. Mime-Version: 1.0 (Apple Message framework v1278) Content-Type: text/plain; charset=us-ascii From: Alexander Graf In-Reply-To: <1366974299-17877-1-git-send-email-pranavkumar@linaro.org> Date: Fri, 26 Apr 2013 13:19:50 +0200 Cc: linux-arm-kernel@lists.infradead.org, linaro-kernel@lists.linaro.org, patches@linaro.org, "linux-kernel@vger.kernel.org List" , kvmarm@lists.cs.columbia.edu, Peter Maydell Content-Transfer-Encoding: 8BIT Message-Id: References: <1366974299-17877-1-git-send-email-pranavkumar@linaro.org> To: Pranavkumar Sawargaonkar X-Mailer: Apple Mail (2.1278) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1602 Lines: 28 On 26.04.2013, at 13:04, Pranavkumar Sawargaonkar wrote: > This patch-set implements early printk support for virtio console devices without using any hypercalls. > > The current virtio early printk code in kernel expects that hypervisor will provide some mechanism generally a hypercall to support early printk. This patch-set does not break existing hypercall based early print support. > > This implementation adds: > 1. Early writeonly register named early_wr in virtio console's config space. > 2. Host feature flags namely VIRTIO_CONSOLE_F_EARLY_WRITE for telling guest about early-write capability in console device. > > Early write mechanism: > 1. When a guest wants to out some character, it has to simply write the character to early_wr register in config space of virtio console device. I won't nack this patch set, but I'll definitely express that I'm not happy with it. MMIO registers are handled by a different layer than the virtio console itself. After the virtio refactoring in QEMU, they will be completely separate drivers. So we'll be in a similar mess with early printk as we are on the s390-virtio machine, where early printk is done through hypercalls and thus we can't directly link it to the console output. I still don't see what the issue is with just implementing a small irq-less virtio driver for early printk. 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/