From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 46442C41514 for ; Tue, 27 Aug 2019 02:13:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 266952080C for ; Tue, 27 Aug 2019 02:13:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728727AbfH0CNy convert rfc822-to-8bit (ORCPT ); Mon, 26 Aug 2019 22:13:54 -0400 Received: from bilbo.ozlabs.org ([203.11.71.1]:57203 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726487AbfH0CNx (ORCPT ); Mon, 26 Aug 2019 22:13:53 -0400 Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mail.ozlabs.org (Postfix) with ESMTPSA id 46HXVR3PjFz9s7T; Tue, 27 Aug 2019 12:13:51 +1000 (AEST) From: Michael Ellerman To: Christophe Leroy , Benjamin Herrenschmidt , Paul Mackerras Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH] powerpc/time: use feature fixup in __USE_RTC() instead of cpu feature. In-Reply-To: References: <55c267ac6e0cd289970accfafbf9dda11a324c2e.1566802736.git.christophe.leroy@c-s.fr> <87blwc40i4.fsf@concordia.ellerman.id.au> Date: Tue, 27 Aug 2019 12:13:51 +1000 Message-ID: <87v9uj2w4g.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Christophe Leroy writes: > Le 26/08/2019 à 13:41, Michael Ellerman a écrit : >> Christophe Leroy writes: >>> sched_clock(), used by printk(), calls __USE_RTC() to know >>> whether to use realtime clock or timebase. >>> >>> __USE_RTC() uses cpu_has_feature() which is initialised by >>> machine_init(). Before machine_init(), __USE_RTC() returns true, >>> leading to a program check exception on CPUs not having realtime >>> clock. >>> >>> In order to be able to use printk() earlier, use feature fixup. >>> Feature fixups are applies in early_init(), enabling the use of >>> printk() earlier. >>> >>> Signed-off-by: Christophe Leroy >>> --- >>> arch/powerpc/include/asm/time.h | 9 ++++++++- >>> 1 file changed, 8 insertions(+), 1 deletion(-) >> >> The other option would be just to make this a compile time decision, eg. >> add CONFIG_PPC_601 and use that to gate whether we use RTC. > > Euh ... yes OK, why not. And that would help simplify many places in the > code. I can propose something in that direction, but it will be a bigger > change. Thanks. >> Given how many 601 users there are, maybe 1?, I think that would be a >> simpler option and avoids complicating the code / binary for everyone >> else. > > However this patch doesn't complicate things more than it was with > cpu_has_feature() which does exactly the same but using static keys, > does it ? It's more complicated in that it's not using cpu_has_feature() it's doing some custom thing that is not used anywhere else. But yeah I guess it's not much extra complication. cheers