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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS 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 BCED0C28CBC for ; Wed, 6 May 2020 16:08:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9646F208CA for ; Wed, 6 May 2020 16:08:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588781308; bh=RUPKmgvzIwl7nzkcthRflNLgzgyC/doSCD1kpStngP8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=mvua8ozu+I65GOnYLGK9s/EgEiv0wjKQSQS8jWsX/vuE+xle63SJOmZj9Kmt+4tBm 0OX3OrMc2RL64EFvlzhTOlHbCwnlGaHTVwzfDmdePqDw6wTlrilcalWYBfLCEv9VXu L0M/K40N0yhZaV8y5OimWClA0ClRCgDGEfwOlYGY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729888AbgEFQI2 (ORCPT ); Wed, 6 May 2020 12:08:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:52152 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729418AbgEFQI1 (ORCPT ); Wed, 6 May 2020 12:08:27 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 783FA208CA; Wed, 6 May 2020 16:08:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588781305; bh=RUPKmgvzIwl7nzkcthRflNLgzgyC/doSCD1kpStngP8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=yFJ0fpYwHFamK+0jKKlAvfpnsD6fl/5v/8V0nks6Gg+R0RjmAuTB1t0IR/eKV855z AJ0aPTBQY4/T4bj8V0ZRfCGmm8BWHSitGYFzl7khaMiP22Qk5TThwnDC7niVCWono6 /HSI/rPrq0hixgsNr4GKhU4fxtYcLt6Jyg8g6CUY= Date: Wed, 6 May 2020 18:08:23 +0200 From: Greg Kroah-Hartman To: Mikulas Patocka Cc: Richard Henderson , Ivan Kokshaysky , Matt Turner , linux-alpha@vger.kernel.org, Sinan Kaya , Arnd Bergmann , linux-serial@vger.kernel.org, linux-rtc@vger.kernel.org Subject: Re: [PATCH 2/2 v2] alpha: add a delay before serial port read Message-ID: <20200506160823.GA3559699@kroah.com> References: <20200506114711.GB3024358@kroah.com> <20200506154938.GA3537174@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-rtc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rtc@vger.kernel.org On Wed, May 06, 2020 at 11:57:08AM -0400, Mikulas Patocka wrote: > > > On Wed, 6 May 2020, Greg Kroah-Hartman wrote: > > > On Wed, May 06, 2020 at 11:29:29AM -0400, Mikulas Patocka wrote: > > > > > > > > > On Wed, 6 May 2020, Greg Kroah-Hartman wrote: > > > > > > > > Index: linux-stable/drivers/tty/serial/8250/8250_port.c > > > > > =================================================================== > > > > > --- linux-stable.orig/drivers/tty/serial/8250/8250_port.c 2020-05-06 08:25:19.000000000 +0200 > > > > > +++ linux-stable/drivers/tty/serial/8250/8250_port.c 2020-05-06 09:04:17.000000000 +0200 > > > > > @@ -442,6 +442,10 @@ static unsigned int mem32be_serial_in(st > > > > > > > > > > static unsigned int io_serial_in(struct uart_port *p, int offset) > > > > > { > > > > > +#ifdef CONFIG_ALPHA > > > > > +/* we need a small delay, the Alpha Avanti chipset locks up with back-to-back accesses */ > > > > > + ndelay(300); > > > > > +#endif > > > > > > > > We really do not like #ifdef in .c files, especially ones that cause a > > > > coding style violation :) > > > > > > > > Why can't you do this as a quirk for this specific chipset? You should > > > > tie it to the serial port hardware type, not to the CPU type. > > > > > > > > thanks, > > > > > > > > greg k-h > > > > > > Do you want this patch? It enables the delay based on the specific PCI-ISA > > > bridge. > > > > > > There is still "#if defined(CONFIG_ALPHA) && defined(CONFIG_PCI)" because > > > if we want to reference a variable defined by the PCI subsystem in the > > > arch/alpha tree, we must do it conditionally. If you want to get rid of > > > these #ifs, please describe how. > > > > > > Mikulas > > > > > > > > > From: Mikulas Patocka > > > > > > The patch 92d7223a74235054f2aa7227d207d9c57f84dca0 ("alpha: io: reorder > > > barriers to guarantee writeX() and iowriteX() ordering #2") broke boot on > > > the Alpha Avanti platform. > > > > > > The patch changes timing between accesses to the ISA bus, in particular, > > > it reduces the time between "write" access and a subsequent "read" access. > > > > > > This causes lock-up when accessing the real time clock and serial ports. > > > > > > This patch fixes the serial ports by adding a small delay before the "inb" > > > instruction. > > > > > > Signed-off-by: Mikulas Patocka > > > Fixes: 92d7223a7423 ("alpha: io: reorder barriers to guarantee writeX() and iowriteX() ordering #2") > > > Cc: stable@vger.kernel.org # v4.17+ > > > > > > --- > > > arch/alpha/include/asm/pci.h | 2 ++ > > > arch/alpha/kernel/pci.c | 4 ++++ > > > drivers/tty/serial/8250/8250_core.c | 7 +++++++ > > > drivers/tty/serial/8250/8250_port.c | 3 +++ > > > include/linux/serial_core.h | 1 + > > > 5 files changed, 17 insertions(+) > > > > > > Index: linux-stable/include/linux/serial_core.h > > > =================================================================== > > > --- linux-stable.orig/include/linux/serial_core.h 2020-05-06 17:16:28.000000000 +0200 > > > +++ linux-stable/include/linux/serial_core.h 2020-05-06 17:16:28.000000000 +0200 > > > @@ -154,6 +154,7 @@ struct uart_port { > > > > > > /* quirks must be updated while holding port mutex */ > > > #define UPQ_NO_TXEN_TEST BIT(0) > > > +#define UPQ_DELAY_BEFORE_READ BIT(1) > > > > > > unsigned int read_status_mask; /* driver specific */ > > > unsigned int ignore_status_mask; /* driver specific */ > > > Index: linux-stable/drivers/tty/serial/8250/8250_core.c > > > =================================================================== > > > --- linux-stable.orig/drivers/tty/serial/8250/8250_core.c 2020-05-06 17:16:28.000000000 +0200 > > > +++ linux-stable/drivers/tty/serial/8250/8250_core.c 2020-05-06 17:16:28.000000000 +0200 > > > @@ -37,6 +37,9 @@ > > > #ifdef CONFIG_SPARC > > > #include > > > #endif > > > +#if defined(CONFIG_ALPHA) && defined(CONFIG_PCI) > > > +#include > > > +#endif > > > > Don't need the #if for this. > > You're right. > > > > #include > > > > > > @@ -490,6 +493,10 @@ static void univ8250_rsa_support(struct > > > static inline void serial8250_apply_quirks(struct uart_8250_port *up) > > > { > > > up->port.quirks |= skip_txen_test ? UPQ_NO_TXEN_TEST : 0; > > > +#if defined(CONFIG_ALPHA) && defined(CONFIG_PCI) > > > + if (alpha_serial_port_needs_delay) > > > + up->port.quirks |= UPQ_DELAY_BEFORE_READ; > > > +#endif > > > > Why is a #define needed here? > > > > You can do this same type of change without any #ifdefs in any .c files > > and that would be much nicer. > > Because alpha_serial_port_needs_delay is defined only on Alpha - so we > need to guard accesses to it with #ifdef CONFIG_ALPHA - otherwise the > kernel wouldn't link on non-Alpha platforms. > > Should I make it defined for all architectures? Yes, it's not the first time we have had to do things like this :) But, there is no other way to detect this based on hardware signatures/types instead? That is usually the best way to do it, right? thanks, greg k-h