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 A4633EE49A3 for ; Wed, 23 Aug 2023 14:49:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236662AbjHWOtQ (ORCPT ); Wed, 23 Aug 2023 10:49:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47242 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236663AbjHWOtQ (ORCPT ); Wed, 23 Aug 2023 10:49:16 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A7AD5E6A; Wed, 23 Aug 2023 07:49:11 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 3D0E96629C; Wed, 23 Aug 2023 14:49:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6C4BEC433C8; Wed, 23 Aug 2023 14:49:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1692802150; bh=9ljjf0tIGNJOKnhwUF512cYAgRc8CmDoikN3TdZHz20=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=fT7n6Pj6ekWBHvDUQ85AfGyy00SxvgvWDHw2ExOuyCLtldknzj8fnZRbHe0OyVFso nG6ff6sf+hEmcgJEPfB5xb5/O7KQ5mtTo3NOv561yMdDg1AW8lhBNWQrvVqn4bLgi0 fpzfsIo5FZ+Up1kRYo8/Ea7ChwVhd/cbE+e2O0aa6718Lj5OyjuWI6jL4zFFrwxQPb CAdyVVUzHzCvksdQxNiAo4fENQ+mAUoGImgsiEwYM2pyPQ0w4VFnXDtGACnujpxzFJ HY9th7aY1xjDza5a5NFDRBlkOMRWkndoXr0pvAmCM7Eew36BRLnoA0iH18Anj1IZNe jiPw3nN+VrLUA== Date: Wed, 23 Aug 2023 16:49:05 +0200 From: Andi Shyti To: Andy Shevchenko Cc: Geert Uytterhoeven , Biju Das , Guenter Roeck , Heikki Krogerus , Greg Kroah-Hartman , linux-usb@vger.kernel.org, Geert Uytterhoeven , Dmitry Torokhov , linux-renesas-soc@vger.kernel.org, "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Rob Herring , Conor Dooley , Frank Rowand Subject: Re: [PATCH 2/4] usb: typec: tcpci_rt1711h: Convert enum->pointer for data in the match tables Message-ID: <20230823144905.mep6w6fctwcxxrhz@intel.intel> References: <20230820184402.102486-3-biju.das.jz@bp.renesas.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org Hi, On Tue, Aug 22, 2023 at 03:08:38PM +0300, Andy Shevchenko wrote: > On Tue, Aug 22, 2023 at 02:00:05PM +0200, Geert Uytterhoeven wrote: > > On Tue, Aug 22, 2023 at 1:44 PM Andy Shevchenko > > wrote: > > > On Tue, Aug 22, 2023 at 09:21:19AM +0200, Geert Uytterhoeven wrote: > > > > On Mon, Aug 21, 2023 at 7:09 PM Andy Shevchenko > > > > wrote: > > > > > On Mon, Aug 21, 2023 at 05:40:05PM +0200, Geert Uytterhoeven wrote: > > > > > > On Mon, Aug 21, 2023 at 5:25 PM Andy Shevchenko > > > > > > wrote: > > > > > > > On Mon, Aug 21, 2023 at 03:27:43PM +0200, Geert Uytterhoeven wrote: > > > > > > > > On Mon, Aug 21, 2023 at 3:04 PM Andy Shevchenko > > > > > > > > wrote: > > > > > > > > > On Sun, Aug 20, 2023 at 07:44:00PM +0100, Biju Das wrote: > > ... > > > > > > > > > > For all your work likes this as I noted in the reply to Guenter that > > > > > > > > > the couple of the selling points here are: > > > > > > > > > 1) avoidance of the pointer abuse in OF table > > > > > > > > > (we need that to be a valid pointer); > > > > > > > > > > > > > > > > There is no pointer abuse: both const void * (in e.g. of_device_id) > > > > > > > > and kernel_ulong_t (in e.g. i2c_device_id) can be used by drivers > > > > > > > > to store a magic cookie, being either a pointer, or an integer value. > > > > > > > > The same is true for the various unsigned long and void * "driver_data" > > > > > > > > fields in subsystem-specific driver structures. > > > > > > > > > > > > > > (void *)5 is the abuse of the pointer. > > > > > > > We carry something which is not a valid pointer from kernel perspective. > > > > > > > > > > > > But the data field is not required to be a valid pointer. > > > > > > What kind and type of information it represents is specific to the driver. > > > > > > > > > > Where to find necessary information which is not always an integer constant. > > > > > For example, for the driver data that has callbacks it can't be invalid pointer. > > > > > > > > If the driver uses it to store callbacks, of course it needs to be a > > > > valid pointer. But that is internal to the driver. It is not that > > > > we're passing random integer values to a function that expects a > > > > pointer that can actually be dereferenced. > > > > > > > > > Since OF ID table structure is universal, it uses pointers. Maybe you need to > > > > > update it to use plain integer instead? > > > > > > > > It is fairly common in the kernel to use void * to indicate a > > > > driver-specific cookie, being either a real pointer or an integral > > > > value, that is passed verbatim. See also e.g. the "dev" parameter > > > > of request_irq(). > > > > > > Yes, that parameter is void * due to calling kfree(free_irq(...)). > > > So, that's argument for my concerns. > > > > Sorry, I don't understand this comment. > > (kfree(free_irq(...)) is only called in pci_free_irq()?) > > Passing void * for a "driver cookie" makes sense due to possibility of the > passing it to other functions that want to have void * as your example shows. > And that supports my idea of having void * over the unsigned long. I actually agree with Andy here... not much to add to his arguments but if a void * is used as an integer then just change the type. I also was quite puzzled when I started seeing this flow of patches. I would rather prefer to store pointers in u64 variables rather than integers in a pointer. Andi