From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753411Ab1AYNZG (ORCPT ); Tue, 25 Jan 2011 08:25:06 -0500 Received: from mail-ey0-f174.google.com ([209.85.215.174]:49146 "EHLO mail-ey0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751772Ab1AYNZE convert rfc822-to-8bit (ORCPT ); Tue, 25 Jan 2011 08:25:04 -0500 MIME-Version: 1.0 In-Reply-To: <20110125124524.GJ11507@n2100.arm.linux.org.uk> References: <8yad3nlh18e.fsf@huya.qualcomm.com> <20110125102652.GB11507@n2100.arm.linux.org.uk> <20110125124524.GJ11507@n2100.arm.linux.org.uk> Date: Tue, 25 Jan 2011 13:25:02 +0000 Message-ID: Subject: Re: questions about arm trustzone From: Dave Martin To: Russell King - ARM Linux Cc: Santosh Shilimkar , sen wang , David Brown , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 25, 2011 at 12:45 PM, Russell King - ARM Linux wrote: > On Tue, Jan 25, 2011 at 12:24:13PM +0000, Dave Martin wrote: >> Avoiding this complexity is one of the motivations for using r7 for >> the syscall number with CONFIG_EABI (instead of using the SVC comment >> field). > > Your history is not entirely correct. > > I had the kernel side of Thumb userspace support in place long before EABI > came along.  Thumb doesn't have a large enough comment field to store the > Linux syscall number, so to get around that problem, I decided to use r7 > for the syscall number.  You'll find 2.4 kernels support Thumb instructions > in userspace. > > As part of the EABI switch for ARM mode - which created an incompatible > SWI interface anyway, we decided that we could reduce data cache pollution > by eliminating the read of the SWI instruction, so we adopted the r7 > method for ARM EABI mode. > Fair enough -- I was glossing over things a bit and I'm not familiar with all the history. So, I guess there were plenty of other good reasons. Cheers ---Dave From mboxrd@z Thu Jan 1 00:00:00 1970 From: dave.martin@linaro.org (Dave Martin) Date: Tue, 25 Jan 2011 13:25:02 +0000 Subject: questions about arm trustzone In-Reply-To: <20110125124524.GJ11507@n2100.arm.linux.org.uk> References: <8yad3nlh18e.fsf@huya.qualcomm.com> <20110125102652.GB11507@n2100.arm.linux.org.uk> <20110125124524.GJ11507@n2100.arm.linux.org.uk> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, Jan 25, 2011 at 12:45 PM, Russell King - ARM Linux wrote: > On Tue, Jan 25, 2011 at 12:24:13PM +0000, Dave Martin wrote: >> Avoiding this complexity is one of the motivations for using r7 for >> the syscall number with CONFIG_EABI (instead of using the SVC comment >> field). > > Your history is not entirely correct. > > I had the kernel side of Thumb userspace support in place long before EABI > came along. ?Thumb doesn't have a large enough comment field to store the > Linux syscall number, so to get around that problem, I decided to use r7 > for the syscall number. ?You'll find 2.4 kernels support Thumb instructions > in userspace. > > As part of the EABI switch for ARM mode - which created an incompatible > SWI interface anyway, we decided that we could reduce data cache pollution > by eliminating the read of the SWI instruction, so we adopted the r7 > method for ARM EABI mode. > Fair enough -- I was glossing over things a bit and I'm not familiar with all the history. So, I guess there were plenty of other good reasons. Cheers ---Dave