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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, 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 749D9C47093 for ; Tue, 1 Jun 2021 11:42:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 56467610A0 for ; Tue, 1 Jun 2021 11:42:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233739AbhFALnm (ORCPT ); Tue, 1 Jun 2021 07:43:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44398 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230288AbhFALnl (ORCPT ); Tue, 1 Jun 2021 07:43:41 -0400 Received: from ssl.serverraum.org (ssl.serverraum.org [IPv6:2a01:4f8:151:8464::1:2]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DA9F0C061574; Tue, 1 Jun 2021 04:41:59 -0700 (PDT) Received: from ssl.serverraum.org (web.serverraum.org [172.16.0.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ssl.serverraum.org (Postfix) with ESMTPSA id 701912224A; Tue, 1 Jun 2021 13:41:57 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=walle.cc; s=mail2016061301; t=1622547718; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=xC7P/bcFCV2ZCGkF8kjoqn5cfA8HZsmaWEnBxWUHEDM=; b=eNiCyfvWaN/+vfSha991PXVg+RUbyHmmgR0PDUfcscbxStGXX847KmZdGfsRA49Z+JNIUK a+xj7o/h3+JkiKyPGmGscPC5NINmziOPzrYVBqxKhgyB1fbvhYNsWTM+lOBq8RLWllzVKI CrALRlMjL7Wd82QxbvzkulHMl7axo0g= MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Tue, 01 Jun 2021 13:41:57 +0200 From: Michael Walle To: Linus Walleij Cc: Andy Shevchenko , Hans de Goede , Sander Vanheule , Andrew Lunn , Pavel Machek , Rob Herring , Lee Jones , Mark Brown , Greg Kroah-Hartman , "Rafael J . Wysocki" , Bartosz Golaszewski , Linux LED Subsystem , devicetree , "open list:GPIO SUBSYSTEM" , Linux Kernel Mailing List Subject: Re: [PATCH v3 0/6] RTL8231 GPIO expander support In-Reply-To: References: <02bbf73ea8a14119247f07a677993aad2f45b088.camel@svanheule.net> <84352c93f27d7c8b7afea54f3932020e9cd97d02.camel@svanheule.net> User-Agent: Roundcube Webmail/1.4.11 Message-ID: <401805ef27bb273d7aca4f3377b53b07@walle.cc> X-Sender: michael@walle.cc Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am 2021-06-01 12:51, schrieb Linus Walleij: > On Tue, Jun 1, 2021 at 12:18 PM Michael Walle wrote: >> Am 2021-06-01 11:59, schrieb Linus Walleij: > >> > Just regarding all registers/memory cells in a register page >> > as default volatile (which is what we do a lot of the time) >> > has its upsides: bugs like this doesn't happen. >> >> I don't think this is the bug here. If it is really a write-only >> register >> the problem is the read in RMW. Because reading the register will >> return >> the input value instead of the (previously written) output value. > > True that. Write and read semantics differ on the register. > > Volatile is used for this and some other things, > like for example interrupts being cleared when a register > is read so it is strictly read-once. Isn't that what precious is for? > So the regmap config is really important to get right. > > IIUC one of the ambitions around Rust is to encode this > in how memory is specified in the language. (I am still > thinking about whether that is really a good idea or not.) -- -michael