Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932640AbbFENLC (ORCPT ); Fri, 5 Jun 2015 09:11:02 -0400 Received: from eddie.linux-mips.org ([148.251.95.138]:58346 "EHLO cvs.linux-mips.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751703AbbFENK7 (ORCPT ); Fri, 5 Jun 2015 09:10:59 -0400 Date: Fri, 5 Jun 2015 15:10:47 +0200 From: Ralf Baechle To: Leonid Yegoshin , macro@linux-mips.org Cc: linux-mips@linux-mips.org, benh@kernel.crashing.org, will.deacon@arm.com, linux-kernel@vger.kernel.org, markos.chandras@imgtec.com, Steven.Hill@imgtec.com, alexander.h.duyck@redhat.com, davem@davemloft.net Subject: Re: [PATCH 1/3] MIPS: R6: Use lightweight SYNC instruction in smp_* memory barriers Message-ID: <20150605131046.GD26432@linux-mips.org> References: <20150602000818.6668.76632.stgit@ubuntu-yegoshin> <20150602000934.6668.43645.stgit@ubuntu-yegoshin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150602000934.6668.43645.stgit@ubuntu-yegoshin> 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: 1449 Lines: 44 On Mon, Jun 01, 2015 at 05:09:34PM -0700, Leonid Yegoshin wrote: Leonid, to me the biggest technical problem with this patch is that the new Kconfig option is user visible. This is the kind of deeply technical options which exceeds the technical knowledge of most users, so it should probably be driven by a select. We probably also want to enquire how old CPUs from before the invention of the stype field are behaving. If those as I hope for all treat an stype != 0 as stype 0 we could simply drop the option. But we might simply be out of luck - dunno. Maciej, do you have an R4000 / R4600 / R5000 / R7000 / SiByte system at hand to test this? I think we don't need to test that SYNC actually works as intended but the simpler test that SYNC is not causing a illegal instruction exception is sufficient, that is if something like int main(int argc, charg *argv[]) { asm(" .set mips2 \n" " sync 0x10 \n" " sync 0x13 \n" " sync 0x04 \n" " .set mips 0 \n"); return 0; } doesn't crash we should be ok. The kernel's SYNC emulation should already be ok. We ignore the stype field entirely and for a uniprocessor R2000/R3000 that should be just the right thing. Ralf -- 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/