From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752879Ab3LBNFu (ORCPT ); Mon, 2 Dec 2013 08:05:50 -0500 Received: from mail-we0-f171.google.com ([74.125.82.171]:50311 "EHLO mail-we0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752558Ab3LBNFq (ORCPT ); Mon, 2 Dec 2013 08:05:46 -0500 From: Michal Nazarewicz To: Thierry Reding Cc: Laxman Dewangan , Mark Brown , linux-spi@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] spi: tegra: avoid unsigned->signed->unsigned promotion In-Reply-To: <20131129214313.GA18036@mithrandir> Organization: http://mina86.com/ References: <1385745164-10534-1-git-send-email-mpn@google.com> <20131129214313.GA18036@mithrandir> User-Agent: Notmuch/0.15.2+55~geb6e9d8 (http://notmuchmail.org) Emacs/24.3.50.1 (x86_64-unknown-linux-gnu) X-Face: PbkBB1w#)bOqd`iCe"Ds{e+!C7`pkC9a|f)Qo^BMQvy\q5x3?vDQJeN(DS?|-^$uMti[3D*#^_Ts"pU$jBQLq~Ud6iNwAw_r_o_4]|JO?]}P_}Nc&"p#D(ZgUb4uCNPe7~a[DbPG0T~!&c.y$Ur,=N4RT>]dNpd;KFrfMCylc}gc??'U2j,!8%xdD Face: 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 X-PGP: 50751FF4 X-PGP-FP: AC1F 5F5C D418 88F8 CC84 5858 2060 4012 5075 1FF4 X-Hashcash: 1:20:131202:linux-spi@vger.kernel.org::8vyEYi4OsP0/4jlB:0000000000000000000000000000000000000bAv X-Hashcash: 1:20:131202:broonie@kernel.org::XaBxm9fW6APLWlLQ:00000000000000000000000000000000000000000000J3H X-Hashcash: 1:20:131202:ldewangan@nvidia.com::Qu5v6JhmR/aGZC2A:000000000000000000000000000000000000000000gJ9 X-Hashcash: 1:20:131202:linux-kernel@vger.kernel.org::xQ58m+sgd/wOs1Xr:0000000000000000000000000000000003+ds X-Hashcash: 1:20:131202:thierry.reding@gmail.com::X9gT1kTu3P4isKMa:0000000000000000000000000000000000000CUtL X-Hashcash: 1:20:131202:linux-tegra@vger.kernel.org::oLIzhe56Vtzk/pVa:0000000000000000000000000000000000BoVX Date: Mon, 02 Dec 2013 14:05:35 +0100 Message-ID: MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="=-=-=" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-=-= Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable > On Fri, Nov 29, 2013 at 06:12:44PM +0100, Michal Nazarewicz wrote: >> u8 type, which is unsigned, is promoted to int, which is singned, when >> doing a binary shift. Then, on 64-bit machines, it is further promoted >> to unsigned long which may lead to more significant half of the value >> to be all ones. To avoid this, explicitly promote to an unsigned type. On Fri, Nov 29 2013, Thierry Reding wrote: > But I don't think there's a real issue here. Even on 64-bit platforms, > writel() will only write 32-bit registers, and therefore discard the > upper 32 bits. > > I think in general perhaps a more proper fix would be to use only u32 > instead of unsigned long for these cases, since then the problem goes > away. u32 is also the type of the value used by writel() so it makes > perfect sense to use it. Yes, you're absolutely right. I dunno why I missed the fact it's used in writel only. I'll prepare a new patch soon(ish). --=20 Best regards, _ _ .o. | Liege of Serenely Enlightened Majesty of o' \,=3D./ `o ..o | Computer Science, Micha=C5=82 =E2=80=9Cmina86=E2=80=9D Nazarewicz = (o o) ooo +------ooO--(_)--Ooo-- --=-=-= Content-Type: multipart/signed; boundary="==-=-="; micalg=pgp-sha1; protocol="application/pgp-signature" --==-=-= Content-Type: text/plain --==-=-= Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iQIcBAEBAgAGBQJSnIWfAAoJECBgQBJQdR/0N3YQAIY840S8OZ7afX+q9n44AH2R 7lbWi2kQoaBcl3mTx86MxR4qNKoltcHq+syuCjGyv8SIMw0Sod7giQX6iwB+f1Kn fgqQgTw7PYUQQBHwSn/dK1/pudJ4MprcA02MBwS2wQ5yDk9WUnF2k98OkPo4sD8n 2j3/bmLu+89FmKMNDk1QrliV1Oginv/r8004c2r1btN3gr54rjmcc5k3oP0L+i5c GSvjniMvUIC5B6v56p5tKxst+JYblZqZ23vTOK/xTeshtiE8iTYv7msTlu5g2fIs 9mKAZFc/OYlBYMGaRVsgBjnWfCc1Q9DzGPBkvRnP87K8LC8drmCO8fQtJm0rh1KZ D2WO9TT1aRRxTZ7SVkd61VW/jb0xxydZCDkNuat1mPP2q8oZNScWme+akwl4iyk2 NbaTmr2dTjMz2yaxStbihd1hDyyavlYOptfUINBrOFpRNqFSg44ntXKMbQmWRODy Ct41WUBM+1AmGvrr6cgaFp93iqwIe/Dtk6sQL7br8hF0/cTuUt8miM0ddsBWGAOK s+NHsD/Cj/9XQktTfMjFJTwblr2IP5t/5YqbjaN70V0bvpLtE5ylkrdTZOJwKw53 nc/jQynz9b/vZjHrBz1wV7nCjjW/9YuwRuXHoQp7Q2t5RoIiuvMYolinUOaSanVb lPEyZIYSxjKq0vX3agd0 =Zblu -----END PGP SIGNATURE----- --==-=-=-- --=-=-=--