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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id ECFD4C433EF for ; Tue, 22 Feb 2022 20:31:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:Content-Type:References:In-Reply-To:Date:Cc:To:From:Subject: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=8naiUaZZutUDfmakXMm/GAA/vNaoBzWUqhbNO9EDMiY=; b=VEy8Oh7XRzz8wIQCiOf/6OINK+ gYB9oG2/ajl/Ps4GjW7aETb/SOTrmqffxyQR9ZwwJffhJoDWjcxy5sUgLhMFYTv3TALV3S+N6M6ko 7fJe5Ug2EvMVDK220l7G1/YVFPvz9oQ8yx14lqIQONSqcXZ5mZPlUjptFyzSlq0Lrj+qCG/jWClHR fiA6ZJ4XjYLFXzXL3/yI6q1nEf+HWxZL4n91B/1OE4kw4E0lgdLtHg2emj1hmTUGIOhYJ5uX6u3/J T+q7A4Ce/p94rRy18GVJuj3GdpzKpc2dBT22QliUgU1K83Lw5F/dwF07zE2OFPs5Y/+G64pDbTCl6 Qxs8nhlw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nMboz-00BXKd-3b; Tue, 22 Feb 2022 20:31:41 +0000 Received: from relay3.hostedemail.com ([64.99.140.34]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nMbov-00BXJ5-Sw for linux-nvme@lists.infradead.org; Tue, 22 Feb 2022 20:31:39 +0000 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220222_123138_024161_92362953 X-CRM114-Status: GOOD ( 27.47 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.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.