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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DEB6CC433FE for ; Mon, 3 Oct 2022 11:54:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229770AbiJCLyz (ORCPT ); Mon, 3 Oct 2022 07:54:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47304 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229698AbiJCLyv (ORCPT ); Mon, 3 Oct 2022 07:54:51 -0400 Received: from mail-qv1-f46.google.com (mail-qv1-f46.google.com [209.85.219.46]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1338413DF5; Mon, 3 Oct 2022 04:54:50 -0700 (PDT) Received: by mail-qv1-f46.google.com with SMTP id mg6so1449864qvb.10; Mon, 03 Oct 2022 04:54:50 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=1lkZFjQAri374KxB7zXDUvCKUxqNzBm83pCNxaD3+Rg=; b=ewdLXwwaqREFoIQp5aUf52j5ZFe/t5gFNEhDrB0isigfW90zpDT7wgWgkOvkPiq1Mq iYZp9iZj9vBNkRUvFinqU3Mus8PLoi84XdbYjHxGt7WugYujrxEvm7M95SiMwnMRWyha bglLJyn/b28PV/z69I0dBioUxERx/LNyVyHiC5KgUbDli9FmVukuv3E876socrAIqwjq tx2v1IsnmYDTuoG2eOSpMSVjg8G4FbSqbPQnRlBisz7Vkzq9N6frk35k8Gn+lJJZXHdX y0wIY78lu/I3s7ZaLq/aCMnQKXPezq190x1pwQ/LCMDb97N9M3cXjN1JLm9g+lEks89N MVyg== X-Gm-Message-State: ACrzQf3/+acmcBy/3B3iOKqYyFDs6YCL4iz31PqDDXvKfv1o+EpXVl1b 2MxEICKRFnlqa30ffRvIhYzLLwlXNc0dgw0Uulg= X-Google-Smtp-Source: AMsMyM7OsF5YlBA77p2Vey2B2ZDeKYFYlfHfTy13MIDE9YR22EJGB10E/7qRuxxGwywPFEQ740BEkbrflHD8xOWCM+o= X-Received: by 2002:ad4:5beb:0:b0:4af:96ab:21e5 with SMTP id k11-20020ad45beb000000b004af96ab21e5mr15845072qvc.85.1664798088934; Mon, 03 Oct 2022 04:54:48 -0700 (PDT) MIME-Version: 1.0 References: <20220928105746.51208-1-andriy.shevchenko@linux.intel.com> <20220928105746.51208-2-andriy.shevchenko@linux.intel.com> In-Reply-To: From: "Rafael J. Wysocki" Date: Mon, 3 Oct 2022 13:54:37 +0200 Message-ID: Subject: Re: [PATCH v2 1/5] device property: Keep dev_fwnode() and dev_fwnode_const() separate To: Greg Kroah-Hartman Cc: Sakari Ailus , Andy Shevchenko , Heikki Krogerus , Bjorn Andersson , Prashant Malani , linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, Daniel Scally , "Rafael J. Wysocki" Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Fri, Sep 30, 2022 at 4:43 PM Greg Kroah-Hartman wrote: > > On Fri, Sep 30, 2022 at 02:30:53PM +0000, Sakari Ailus wrote: > > Hi Greg, > > > > On Wed, Sep 28, 2022 at 01:05:20PM +0200, Greg Kroah-Hartman wrote: > > > On Wed, Sep 28, 2022 at 01:57:42PM +0300, Andy Shevchenko wrote: > > > > It's not fully correct to take a const parameter pointer to a struct > > > > and return a non-const pointer to a member of that struct. > > > > > > > > Instead, introduce a const version of the dev_fwnode() API which takes > > > > and returns const pointers and use it where it's applicable. > > > > > > > > Suggested-by: Sakari Ailus > > > > Fixes: aade55c86033 ("device property: Add const qualifier to device_get_match_data() parameter") > > > > Signed-off-by: Andy Shevchenko > > > > Acked-by: Heikki Krogerus > > > > Reviewed-by: Sakari Ailus > > > > --- > > > > drivers/base/property.c | 11 +++++++++-- > > > > include/linux/property.h | 3 ++- > > > > 2 files changed, 11 insertions(+), 3 deletions(-) > > > > > > > > diff --git a/drivers/base/property.c b/drivers/base/property.c > > > > index 4d6278a84868..699f1b115e0a 100644 > > > > --- a/drivers/base/property.c > > > > +++ b/drivers/base/property.c > > > > @@ -17,13 +17,20 @@ > > > > #include > > > > #include > > > > > > > > -struct fwnode_handle *dev_fwnode(const struct device *dev) > > > > +struct fwnode_handle *dev_fwnode(struct device *dev) > > > > { > > > > return IS_ENABLED(CONFIG_OF) && dev->of_node ? > > > > of_fwnode_handle(dev->of_node) : dev->fwnode; > > > > } > > > > EXPORT_SYMBOL_GPL(dev_fwnode); > > > > > > > > +const struct fwnode_handle *dev_fwnode_const(const struct device *dev) > > > > +{ > > > > + return IS_ENABLED(CONFIG_OF) && dev->of_node ? > > > > + of_fwnode_handle(dev->of_node) : dev->fwnode; > > > > +} > > > > +EXPORT_SYMBOL_GPL(dev_fwnode_const); > > > > > > Ick, no, this is a mess. > > > > > > Either always return a const pointer, or don't. Ideally always return a > > > const pointer, so all we really need is: > > > > > > const struct fwnode_handle *dev_fwnode(const struct device *dev); > > > > > > right? > > > > > > Yes, it will take some unwinding backwards to get there, but please do > > > that instead of having 2 different functions where the parameter type is > > > part of the function name. This isn't the 1980's... > > > > The problem with this approach is that sometimes non-const fwnode_handles > > are needed. On OF, for instance, anything that has something to do with > > refcounting requires this. Software nodes as well. > > If they are writable, then yes, let's keep them writable, and not create > two function paths where we have to pick and choose. > > > One option which I suggested earlier was to turn dev_fwnode() into a macro > > and use C11 _Generic() to check whether the device is const or not. > > As much fun as that would be, I don't think it would work well. > > Although, maybe it would, have an example of how that would look? > > I ask as I just went through a large refactoring of the kobject layer to > mark many things const * and I find it a bit "sad" that functions like > this: > static inline struct device *kobj_to_dev(const struct kobject *kobj) > { > return container_of(kobj, struct device, kobj); > } > have the ability to take a read-only pointer and spit out a writable one > thanks to the pointer math in container_of() with no one being the > wiser. Well, is this really a problem? After all, if an immutable structure is embedded in another one, that doesn't automatically imply that the containing structure has to be immutable too. Hence, a const pointer to the inner structure doesn't automatically yield a const pointer to the outer one. > > Being able to turn struct device pointers const is certainly not worth > > violating constness properties. > > Agreed, but we can do better...