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=-3.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 E14DBC2D0A3 for ; Thu, 12 Nov 2020 16:10:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 89D7E22227 for ; Thu, 12 Nov 2020 16:10:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728816AbgKLQKs (ORCPT ); Thu, 12 Nov 2020 11:10:48 -0500 Received: from mail.baikalelectronics.com ([87.245.175.226]:48422 "EHLO mail.baikalelectronics.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728414AbgKLQKs (ORCPT ); Thu, 12 Nov 2020 11:10:48 -0500 Received: from localhost (unknown [127.0.0.1]) by mail.baikalelectronics.ru (Postfix) with ESMTP id 028F4803017D; Thu, 12 Nov 2020 16:10:45 +0000 (UTC) X-Virus-Scanned: amavisd-new at baikalelectronics.ru Received: from mail.baikalelectronics.ru ([127.0.0.1]) by localhost (mail.baikalelectronics.ru [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id gg4bBmqmtuiN; Thu, 12 Nov 2020 19:10:44 +0300 (MSK) Date: Thu, 12 Nov 2020 19:10:43 +0300 From: Serge Semin To: Miquel Raynal CC: Serge Semin , Vignesh Raghavendra , , , kernel test robot , Subject: Re: drivers/mtd/maps/physmap-bt1-rom.c:78:18: sparse: sparse: cast removes address space '__iomem' of expression Message-ID: <20201112161043.brhpuo7rykdip3hs@mobilestation> References: <202011021254.XC70BaQT-lkp@intel.com> <20201110113827.hl5i27cpl6exo3md@mobilestation> <20201110163556.3e3423f6@xps13> <20201111192259.ovdyjcuue7fx2bqa@mobilestation> <20201112092715.7e466405@xps13> <8cdc6166-7183-c8a9-5c27-93a511e6471a@ti.com> <20201112152739.r4673zyeixkcwukx@mobilestation> <20201112164301.60032276@xps13> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20201112164301.60032276@xps13> X-ClientProxiedBy: MAIL.baikal.int (192.168.51.25) To mail (192.168.51.25) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 12, 2020 at 04:43:01PM +0100, Miquel Raynal wrote: > Hi Serge, > > Serge Semin wrote on Thu, 12 Nov > 2020 18:27:39 +0300: > > > Hello Vignesh > > > > On Thu, Nov 12, 2020 at 08:30:42PM +0530, Vignesh Raghavendra wrote: > > > > > > > > > On 11/12/20 1:57 PM, Miquel Raynal wrote: > > > > Hi Sergey, > > > > > > > > Serge Semin wrote on Wed, 11 Nov > > > > 2020 22:22:59 +0300: > > > > > > > >> On Tue, Nov 10, 2020 at 04:35:56PM +0100, Miquel Raynal wrote: > > > >>> Hi Serge, > > > >>> > > > >>> Serge Semin wrote on Tue, 10 Nov > > > >>> 2020 14:38:27 +0300: > > > >>> > > > >>>> Hello Miquel, > > > >>>> > > > >>>> A situation noted by the warning below won't cause any problem because > > > >>>> the casting is done to a non-dereferenced variable. It is utilized > > > >>>> as a pointer bias later in that function. Shall we just ignore the > > > >>>> warning or still fix it somehow? > > > >>> > > > >> > > > >>> Do you think the cast to a !__iomem value is mandatory here? > > > >> > > > >> It's not mandatory to have the casting with no __iomem, but wouldn't > > > >> doing like this: > > > >> + shift = (ssize_t __iomem)src & 0x3; > > > >> be looking weird? Really, is there a good way to somehow extract the first > > > >> two bits of a __iomem pointer without getting the sparse warning? > > > > > > > > I asked around me, what about trying uintptr_t? > > > > > > > > > > > > One more way is to use __force to tell sparse that this casting is > > > intentional: > > > > > > shift = (__force ssize_t)src & 0x3; > > > > Oh, great! That solution is actually much better than using some > > currently unexplained sparse peculiarity! I was thinking about applying > > some other attribute, but __force just didn't come to my mind. Thank > > you very much for the suggestion. I'll post the fix with the solution > > suggested by you. > > Is the ssize_t cast the right one btw? I would definitely prefer an > unsigned type here. The reason of me deciding to use the ssize_t type here was to prevent the types casting across the "shift", "chunk" and "len" variables within this method. It seemed a bit better than having a standard type like "unsigned int" here seeing the ssize_t type width won't exceed the long type size anyway. Moreover since the "len" variable has got the ssize_t type and I couldn't change it (the method is the map_info callback), I've decided to stick with what is available and defined "shift" and "chunk" as ssize_t-es. Another callback method bt1_rom_map_read() in his module has been designed in the same way. Do you think it's better to change it in favor of using a different type like "unsigned int" here anyway? If so for unification I'd need to change bt1_rom_map_read() (though the "shift" variable has been defined as "unsigned long" there in the first place because the offs argument has got that type). What to do with the __force attribute here? It does seem appropriate even if for some mystical reasons we haven't got the sparse warning for the unsigned types. -Sergey > > Thanks, > Miquèl