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 32AA8C433F5 for ; Mon, 3 Oct 2022 11:02:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229660AbiJCLCh (ORCPT ); Mon, 3 Oct 2022 07:02:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46002 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229612AbiJCLCd (ORCPT ); Mon, 3 Oct 2022 07:02:33 -0400 Received: from mga17.intel.com (mga17.intel.com [192.55.52.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A33A157BE9; Mon, 3 Oct 2022 04:02:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1664794945; x=1696330945; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=wqw4e70MNDpcLBlciYTdcT/eeoS9T0H008Z1ezp9K3o=; b=g+VYm8UA0cW5fPYPJBmLOI3A+NggYpdAIzGC6wF+23qiErEibdcD9r3y wj7vc1SGnrduEd7OJXz/+WB/Uwi9Hv2trVYzh2UTjIglotBYz/krHWgm7 FWfjsw8ysZk92C7DdWvIvYvtjvOnV0c1ULcn1LNVmoL5kQ3XBBgxZnLft P0TMk+HCkSB8TOqX0Vv35ew1zNOo4Pgin0WRBNFWDucpSjtDYxods7A/G 7lIH5pKDd5D1JUAlNDeRBFvaNTWJVio48ON0ZsIXBiFgvES6D95M25D/n hF9KhraTr7QXQ2YuCnfA7/ffWVTjxYH9ZtK/uLMzHoR/ZxMM+V/G/8HBP A==; X-IronPort-AV: E=McAfee;i="6500,9779,10488"; a="282974445" X-IronPort-AV: E=Sophos;i="5.93,365,1654585200"; d="scan'208";a="282974445" Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Oct 2022 04:02:25 -0700 X-IronPort-AV: E=McAfee;i="6500,9779,10488"; a="574586386" X-IronPort-AV: E=Sophos;i="5.93,365,1654585200"; d="scan'208";a="574586386" Received: from punajuuri.fi.intel.com (HELO paasikivi.fi.intel.com) ([10.237.72.43]) by orsmga003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Oct 2022 04:02:22 -0700 Received: from paasikivi.fi.intel.com (localhost [127.0.0.1]) by paasikivi.fi.intel.com (Postfix) with SMTP id 0575B2033F; Mon, 3 Oct 2022 14:02:20 +0300 (EEST) Date: Mon, 3 Oct 2022 11:02:19 +0000 From: Sakari Ailus To: Greg Kroah-Hartman Cc: 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" Subject: Re: [PATCH v2 1/5] device property: Keep dev_fwnode() and dev_fwnode_const() separate Message-ID: References: <20220928105746.51208-1-andriy.shevchenko@linux.intel.com> <20220928105746.51208-2-andriy.shevchenko@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Greg, On Fri, Sep 30, 2022 at 04:43:19PM +0200, 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? Similar to what container_of() could be, see below. We could also partially revert aade55c86033bee868a93e4bf3843c9c99e84526 which (also) made dev_fwnode() argument const (which is the source of the issue). > > 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. Yeah, container_of() is dangerous, especially in macros. It could of course be made safer. Something like this: I can respin it, back in 2017 I got no replies. > > > Being able to turn struct device pointers const is certainly not worth > > violating constness properties. > > Agreed, but we can do better... -- Regards, Sakari Ailus