From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Tue, 01 Oct 2013 14:54:26 +0200 (CEST) Received: from localhost.localdomain ([127.0.0.1]:42896 "EHLO linux-mips.org" rhost-flags-OK-OK-OK-FAIL) by eddie.linux-mips.org with ESMTP id S6867713Ab3JAMyXvnBOu (ORCPT ); Tue, 1 Oct 2013 14:54:23 +0200 Received: from scotty.linux-mips.net (localhost.localdomain [127.0.0.1]) by scotty.linux-mips.net (8.14.7/8.14.4) with ESMTP id r91CsLus013196; Tue, 1 Oct 2013 14:54:21 +0200 Received: (from ralf@localhost) by scotty.linux-mips.net (8.14.7/8.14.7/Submit) id r91CsLcc013195; Tue, 1 Oct 2013 14:54:21 +0200 Date: Tue, 1 Oct 2013 14:54:21 +0200 From: Ralf Baechle To: Leonid Yegoshin Cc: linux-mips@linux-mips.org, "Steven J. Hill" Subject: Re: 74K/1074K support Message-ID: <20131001125420.GA12616@linux-mips.org> References: <20130925052715.GB473@linux-mips.org> <5249ED1E.4050106@imgtec.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5249ED1E.4050106@imgtec.com> User-Agent: Mutt/1.5.21 (2010-09-15) Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 38083 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: ralf@linux-mips.org Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips On Mon, Sep 30, 2013 at 02:29:02PM -0700, Leonid Yegoshin wrote: > On 09/24/2013 10:27 PM, Ralf Baechle wrote: > >Commit 006a851b10a395955c153a145ad8241494d43688 adds 74K support in c-r4k.c: > > > >+static inline void alias_74k_erratum(struct cpuinfo_mips *c) > >+{ > >+ /* > >+ * Early versions of the 74K do not update the cache tags on a > >+ * vtag miss/ptag hit which can occur in the case of KSEG0/KUSEG > >+ * aliases. In this case it is better to treat the cache as always > >+ * having aliases. > >+ */ > >+ if ((c->processor_id & 0xff) <= PRID_REV_ENCODE_332(2, 4, 0)) > >+ c->dcache.flags |= MIPS_CACHE_VTAG; > >+ if ((c->processor_id & 0xff) == PRID_REV_ENCODE_332(2, 4, 0)) > >+ write_c0_config6(read_c0_config6() | MIPS_CONF6_SYND); > >+ if (((c->processor_id & 0xff00) == PRID_IMP_1074K) && > >+ ((c->processor_id & 0xff) <= PRID_REV_ENCODE_332(1, 1, 0))) { > >+ c->dcache.flags |= MIPS_CACHE_VTAG; > >+ write_c0_config6(read_c0_config6() | MIPS_CONF6_SYND); > >+ } > >+} > > > >But MIPS D-caches are never virtually tagged, so there is nothing in > >the kernel that ever tests the MIPS_CACHE_VTAG flag in a D-cache > >descriptor. > > > >Cargo cult programming at its finest? Or was MIPS_CACHE_ALIASES what > >really was meant to be set? > > > > Ralf > > There is a problem on early versions of 74K/1074K which can be effectively cured by setting MIPS_CACHE_VTAG. > It enforces the needed cache handling. > I hope it will go away as customers replace RTL for newer versions. > But I prefer the patch version from Maciej W. Rozycki, it is more clear. There is nothing in the kernel that _reads_ that flag if it's set in an I-cache descriptor. See: arch/mips/include/asm/cpu-features.h:#define cpu_has_vtag_icache (cpu_data[0].icache.flags & MIPS_CACHE_VTAG) arch/mips/include/asm/cpu-info.h:#define MIPS_CACHE_VTAG 0x00000002 /* Virtually tagged cache */ arch/mips/mm/c-octeon.c: c->icache.flags |= MIPS_CACHE_VTAG; arch/mips/mm/c-octeon.c: c->icache.flags |= MIPS_CACHE_VTAG; arch/mips/mm/c-octeon.c: c->icache.flags |= MIPS_CACHE_VTAG; arch/mips/mm/c-r4k.c: c->dcache.flags |= MIPS_CACHE_VTAG; arch/mips/mm/c-r4k.c: c->dcache.flags |= MIPS_CACHE_VTAG; arch/mips/mm/c-r4k.c: c->icache.flags |= MIPS_CACHE_VTAG; arch/mips/mm/c-r4k.c: c->icache.flags |= MIPS_CACHE_VTAG; arch/mips/mm/c-r4k.c: c->icache.flags & MIPS_CACHE_VTAG ? "VIVT" : "VIPT", There simply is not support whatsoever for virtually tagged D-caches in the kernel, so setting that flag may feel good - but achieves nothing. See, the sole test for the MIPS_CACHE_VTAG above tests it in a D-cache descriptor. So I'm not sure what the intention is. Maybe there is some code that has not yet been merged? Ralf