Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932497AbbFVNMk (ORCPT ); Mon, 22 Jun 2015 09:12:40 -0400 Received: from foss.arm.com ([217.140.101.70]:48685 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754508AbbFVNMd (ORCPT ); Mon, 22 Jun 2015 09:12:33 -0400 Date: Mon, 22 Jun 2015 14:12:28 +0100 From: Will Deacon To: Timur Tabi Cc: Catalin Marinas , "abhimany@codeaurora.org" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] ARM64: TTY: hvc_dcc: Add support for ARM64 dcc Message-ID: <20150622131228.GE1583@arm.com> References: <1434751734-2178-1-git-send-email-timur@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1434751734-2178-1-git-send-email-timur@codeaurora.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2187 Lines: 60 On Fri, Jun 19, 2015 at 11:08:54PM +0100, Timur Tabi wrote: > From: Abhimanyu Kapur > > Add support for debug communications channel based > hvc console for arm64 cpus. I still think we should be disabling userspace access to the DCC if the kernel is using it as its console. > Signed-off-by: Abhimanyu Kapur > Signed-off-by: Timur Tabi > --- > arch/arm64/include/asm/dcc.h | 49 ++++++++++++++++++++++++++++++++++++++++++++ > drivers/tty/hvc/Kconfig | 2 +- > 2 files changed, 50 insertions(+), 1 deletion(-) > create mode 100644 arch/arm64/include/asm/dcc.h > > diff --git a/arch/arm64/include/asm/dcc.h b/arch/arm64/include/asm/dcc.h > new file mode 100644 > index 0000000..f038d61 > --- /dev/null > +++ b/arch/arm64/include/asm/dcc.h > @@ -0,0 +1,49 @@ > +/* Copyright (c) 2014 The Linux Foundation. All rights reserved. > + * > + * This program is free software; you can redistribute it and/or modify > + * it under the terms of the GNU General Public License version 2 and > + * only version 2 as published by the Free Software Foundation. > + * > + * This program is distributed in the hope that it will be useful, > + * but WITHOUT ANY WARRANTY; without even the implied warranty of > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > + * GNU General Public License for more details. > + * > + * A call to __dcc_getchar() or __dcc_putchar() is typically followed by > + * a call to __dcc_getstatus(). We want to make sure that the CPU does > + * not speculative read the DCC status before executing the read or write > + * instruction. That's what the ISBs are for. > + * > + * The 'volatile' ensures that the compiler does not cache the status bits, > + * and instead reads the DCC register every time. > + */ Missing header guards. > +#include > + > +static inline u32 __dcc_getstatus(void) > +{ > + u32 __ret; > + > + asm volatile("mrs %0, mdccsr_el0" : "=r" (__ret) > + : : "cc"); You don't need the "cc" clobber. Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/