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 618B5C4332F for ; Fri, 30 Sep 2022 14:43:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231384AbiI3On2 (ORCPT ); Fri, 30 Sep 2022 10:43:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46418 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231356AbiI3On0 (ORCPT ); Fri, 30 Sep 2022 10:43:26 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 95961110B1A; Fri, 30 Sep 2022 07:43:24 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 4ED32B828F5; Fri, 30 Sep 2022 14:43:23 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8FA7FC433C1; Fri, 30 Sep 2022 14:43:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1664549002; bh=DB2pKYXZ8BUgPkKBVEjgw5iP+LkB2BXyoqa3AHEDai4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=T/Odph4o2NcgAsdbjSjVEUOWDtTp9Vb9v8I2iMQM8l78BhKrOJ5+x5u85fSx8cpk5 ShOHMe9MTMcoWgT6y/85fXhLO5yKaQfd4CocqnkDtepnIhYbIdoHQeyPfjPhiT2Wmh CCb1os2WrlCGpI626759W+WjijBO9l9aZKBbFTc8= Date: Fri, 30 Sep 2022 16:43:19 +0200 From: Greg Kroah-Hartman To: Sakari Ailus 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-acpi@vger.kernel.org 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. > Being able to turn struct device pointers const is certainly not worth > violating constness properties. Agreed, but we can do better... thanks, greg k-h