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 B334FC433FE for ; Tue, 22 Feb 2022 20:31:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235487AbiBVUcC (ORCPT ); Tue, 22 Feb 2022 15:32:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46174 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235486AbiBVUcB (ORCPT ); Tue, 22 Feb 2022 15:32:01 -0500 Received: from relay4.hostedemail.com (relay4.hostedemail.com [64.99.140.35]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3307B1C907 for ; Tue, 22 Feb 2022 12:31:34 -0800 (PST) Received: from omf10.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 3921423112; Tue, 22 Feb 2022 20:31:33 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: joe@perches.com) by omf10.hostedemail.com (Postfix) with ESMTPA id 212BE3E; Tue, 22 Feb 2022 20:31:31 +0000 (UTC) Message-ID: Subject: Re: [PATCHv3 04/10] linux/kernel: introduce lower_48_bits macro From: Joe Perches To: David Laight , Keith Busch , Christoph Hellwig Cc: "linux-nvme@lists.infradead.org" , "linux-block@vger.kernel.org" , "linux-crypto@vger.kernel.org" , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , "axboe@kernel.dk" , "martin.petersen@oracle.com" , "colyli@suse.de" , Bart Van Assche Date: Tue, 22 Feb 2022 12:31:30 -0800 In-Reply-To: <65fd7d9525b443fcbb15468176fca16a@AcuMS.aculab.com> References: <20220222163144.1782447-1-kbusch@kernel.org> <20220222163144.1782447-5-kbusch@kernel.org> <66a0c8210cf9e7dfcc3fa2d247de1eebd5a8acb7.camel@perches.com> <20220222165045.GA14168@lst.de> <20220222165613.GB1497257@dhcp-10-100-145-180.wdc.com> <603f9243bb9e1c4c50aaec83a527266b48ab9e20.camel@perches.com> <65fd7d9525b443fcbb15468176fca16a@AcuMS.aculab.com> Content-Type: text/plain; charset="ISO-8859-1" User-Agent: Evolution 3.40.4-1ubuntu2 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Stat-Signature: j6sb6dyjbjkt7oik85ducwufi81y7epk X-Rspamd-Server: rspamout01 X-Rspamd-Queue-Id: 212BE3E X-Session-Marker: 6A6F6540706572636865732E636F6D X-Session-ID: U2FsdGVkX19EtqwWf6kiHllY/BwsW7Y4xiMn/fz+NUI= X-HE-Tag: 1645561891-809749 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Tue, 2022-02-22 at 20:09 +0000, David Laight wrote: > From: Joe Perches > > Sent: 22 February 2022 18:43 > > > > On Tue, 2022-02-22 at 08:56 -0800, Keith Busch wrote: > > > On Tue, Feb 22, 2022 at 05:50:45PM +0100, Christoph Hellwig wrote: > > > > On Tue, Feb 22, 2022 at 08:45:53AM -0800, Joe Perches wrote: > > > > > On Tue, 2022-02-22 at 08:31 -0800, Keith Busch wrote: > > > > > > +/ * > > > > > > + * lower_48_bits - return bits 0-47 of a number > > > > > > + * @n: the number we're accessing > > > > > > + */ > > > > > > +#define lower_48_bits(n) ((u64)((n) & 0xffffffffffffull)) > > > > > > > > > > why not make this a static inline function? > > > > > > > > Agreed. > > > > > > Sure, that sounds good to me. I only did it this way to match the > > > existing local convention, but I personally prefer the inline function > > > too. > > > > The existing convention is used there to allow the compiler to > > avoid warnings and unnecessary conversions of a u32 to a u64 when > > shifting by 32 or more bits. > > > > If it's possible to be used with an architecture dependent typedef > > like dma_addr_t, then perhaps it's reasonable to do something like: > > > > #define lower_48_bits(val) \ > > ({ \ > > typeof(val) high = lower_16_bits(upper_32_bits(val)); \ > > typeof(val) low = lower_32_bits(val); \ > > \ > > (high << 16 << 16) | low; \ > > }) > > > > and have the compiler have the return value be an appropriate type. > > The compiler could make a real pigs breakfast of that. Both gcc and clang optimize it just fine. btw: to return the same type the last line should be: (typeof(val))((high << 16 << 16) | low); otherwise the return is sizeof(int) if typeof(val) is not u64 > Oh, did you look for GENMASK([^,]*,[ 0]*) ? No, why? I did look for 47, 0 though. But it's pretty common really. $ git grep -P 'GENMASK(?:_ULL)?\s*\(\s*\d+\s*,\s*0\s*\)' | wc -l 6233 > I'd only use something GENMASK() for bit ranges. > Even then it is often easier to just write the value in hex. Mostly it's the count of the repeated f that's difficult to quickly verify visually. > I think the only time I've written anything like that recently > (last 30 years) was for some hardware registers when the documentation > user 'bit 1' for the most significant bit. Luckily the hardware I've had to deal with never did that. Not even the least significant bit too.