From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Fri, 19 Apr 2013 10:39:53 +0100 Subject: [RFC] arm64: Early printk support for virtio-mmio console devices. In-Reply-To: References: <1366264344-28025-1-git-send-email-pranavkumar@linaro.org> <20130419090558.GA13283@mudshark.cambridge.arm.com> <20130419092752.GB13283@mudshark.cambridge.arm.com> Message-ID: <20130419093953.GD13283@mudshark.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Fri, Apr 19, 2013 at 10:34:56AM +0100, Pranavkumar Sawargaonkar wrote: > On 19 April 2013 15:00, Peter Maydell wrote: > > On 19 April 2013 10:27, Will Deacon wrote: > >> On Fri, Apr 19, 2013 at 10:25:35AM +0100, Pranavkumar Sawargaonkar wrote: > >>> I am not against using 8250 emulation (as far as it solves printk > >>> issues for kernel booting logs), but my point is why not to add early > >>> read-write support for virtio console, which also can be useful in > >>> emulation less mach-virt environment also ? > >> > >> We can have both, but only one of those requires a change to the virtio > >> specification. > > > > I don't think avoiding writing a spec is necessarily a good reason > > for insisting on emulation of a lump of hardware 95% of whose > > capabilities you aren't going to use... > > True. > Also 8250 will require emulation of registers, and i am not sure about > if mach-virt will have any emulation of real hw ? The point of mach-virt is that it is completely parameterised. So, if you're not emulating an 8250, then don't tell the kernel that you have one! Similarly, if you *do* emulate it, then either create a device-tree node for it or pass the appropriate earlyprintk= string on the command line. As far as kvmtool is concerned, we'd probably have a new command-line option for arm64, allowing you to specify the early console device. Will