From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mailapp01.imgtec.com ([195.59.15.196]:61041 "EHLO mailapp01.imgtec.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751680AbbILPLi (ORCPT ); Sat, 12 Sep 2015 11:11:38 -0400 Date: Sat, 12 Sep 2015 08:11:31 -0700 From: Paul Burton To: Ralf Baechle CC: , Markos Chandras , , Subject: Re: [PATCH 5/6] MIPS: CONFIG_MIPS_MT_SMP should depend upon CPU_MIPSR2 Message-ID: <20150912151131.GA3831@NP-P-BURTON> References: <1438814560-19821-1-git-send-email-paul.burton@imgtec.com> <1438814560-19821-6-git-send-email-paul.burton@imgtec.com> <20150912101638.GA7422@linux-mips.org> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20150912101638.GA7422@linux-mips.org> Sender: stable-owner@vger.kernel.org List-ID: On Sat, Sep 12, 2015 at 12:16:39PM +0200, Ralf Baechle wrote: > > config MIPS_MT_SMP > > bool "MIPS MT SMP support (1 TC on each available VPE)" > > - depends on SYS_SUPPORTS_MULTITHREADING > > + depends on SYS_SUPPORTS_MULTITHREADING && CPU_MIPSR2 > > Right now this line is > > depends on SYS_SUPPORTS_MULTITHREADING && !CPU_MIPSR6 > > which I believe is correct. The MT SMP support aka VSMP had been > carefully crafted to work on older ASEs that is all use of MIPS MT > instructions or features was carefully protected by cpu_has_mipsmt > or similar. I disagree. The "background" section in the introduction to the MT ASE spec (MD00376, revision 1.12) reads: > Multi-threading, or the concurrent presence of multiple active threads > or contexts of execution on the same CPU, is an increasingly > widely-used technique for tolerating memory and execution latency and > for getting higher utilization out of processor functional units. The > MIPS® Multi-threading (MT) Module is an extension to Release 2 (and > newer) of the MIPS32® Architecture which provides a framework for > multi-threading the MIPS processor architecture. MT is quite clearly an extension to r2. The MT bit in Config3 has this note in the MIPS32 PRA (MD00088, revision 6.01): > For Release 6 and MIPS after, this bit must be 0. Thus MT is an option from r2 <= ISA < r6. The current !CPU_MIPSR6 constraint in Kconfig only enforces half of that. Depending upon CPU_MIPSR2 would enforce the whole. Thanks, Paul