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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 994A2C48BE6 for ; Wed, 16 Jun 2021 08:48:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 855316109D for ; Wed, 16 Jun 2021 08:48:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232095AbhFPIuJ convert rfc822-to-8bit (ORCPT ); Wed, 16 Jun 2021 04:50:09 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:32394 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232054AbhFPIuI (ORCPT ); Wed, 16 Jun 2021 04:50:08 -0400 Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-123-neNOsckdMEaptkxvYReotQ-1; Wed, 16 Jun 2021 09:48:00 +0100 X-MC-Unique: neNOsckdMEaptkxvYReotQ-1 Received: from AcuMS.Aculab.com (10.202.163.6) by AcuMS.aculab.com (10.202.163.6) with Microsoft SMTP Server (TLS) id 15.0.1497.18; Wed, 16 Jun 2021 09:47:59 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.018; Wed, 16 Jun 2021 09:47:59 +0100 From: David Laight To: 'liweihang' , "davem@davemloft.net" , "kuba@kernel.org" , "andrew@lunn.ch" , "hkallweit1@gmail.com" CC: "netdev@vger.kernel.org" , Linuxarm , liangwenpeng , "quentin.schulz@bootlin.com" , "antoine.tenart@bootlin.com" Subject: RE: [PATCH net-next 8/8] net: phy: use '__packed' instead of '__attribute__((__packed__))' Thread-Topic: [PATCH net-next 8/8] net: phy: use '__packed' instead of '__attribute__((__packed__))' Thread-Index: AQHXXoypAvtg6ISf/0iVeDQMIX2EFasWVTWA Date: Wed, 16 Jun 2021 08:47:59 +0000 Message-ID: <30f32e888f9e40a5b78549609df936d0@AcuMS.aculab.com> References: <1623393419-2521-1-git-send-email-liweihang@huawei.com> <1623393419-2521-9-git-send-email-liweihang@huawei.com> <7c07e865cfeb467c8f6a9eca218c5fdf@AcuMS.aculab.com> In-Reply-To: Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: liweihang > Sent: 16 June 2021 07:17 > > On 2021/6/14 22:28, David Laight wrote: > > From: Weihang Li > >> Sent: 11 June 2021 07:37 > >> > >> Prefer __packed over __attribute__((__packed__)). > >> > >> Signed-off-by: Wenpeng Liang > >> Signed-off-by: Weihang Li > >> --- > >> drivers/net/phy/mscc/mscc_ptp.h | 4 ++-- > >> 1 file changed, 2 insertions(+), 2 deletions(-) > >> > >> diff --git a/drivers/net/phy/mscc/mscc_ptp.h b/drivers/net/phy/mscc/mscc_ptp.h > >> index da34653..01f78b4 100644 > > ... > >> /* Represents an entry in the timestamping FIFO */ > >> struct vsc85xx_ts_fifo { > >> u32 ns; > >> u64 secs:48; > >> u8 sig[16]; > >> -} __attribute__((__packed__)); > >> +} __packed; > > > > Hmmmm I'd take some convincing that 'u64 secs:48' is anything > > other than 'implementation defined'. > > So using it to map a hardware structure seems wrong. > > > > If this does map a hardware structure it ought to have > > 'endianness' annotations. > > If it doesn't then why the bitfield and why packed? > > > > David > > Hi David, > > Thank you for your attention. You are right, I found the contents of structure > vsc85xx_ts_fifo is got from hardware. But I'm not sure if any issues or warnings > will be introduced into this driver after just changing 'u64 secs:48' to '__be64 > secs:48'. I've just checked what this structure looks like - see https://godbolt.org/z/h4EqbMoso Without any 'packed' annotations 'u64 secs:48' is aligned to an 8 byte boundary, but is only 6 bytes wide (I don't use bitfields) so the offset of 'sig' is 6 more than 'secs'. But the size of the whole structure looks wrong. I'd expect a hardware fifo so be a power of 2 big. This one is 26 bytes (as above) or 28 bytes if the 'packed' is only applied to 'secs' (which removed the 4 byte pad before it while still allowing aligned 4-byte accesses to the structure. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)