From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marc Kleine-Budde Date: Mon, 20 Jan 2014 12:05:43 +0000 Subject: Re: [PATCH v5] can: add Renesas R-Car CAN driver Message-Id: <52DD1117.5030406@pengutronix.de> MIME-Version: 1 Content-Type: multipart/mixed; boundary="JktNm4E6ofJADlcojgfVkjSBVD1glpcxU" List-Id: References: <201312270037.15822.sergei.shtylyov@cogentembedded.com> <52DD0CC1.70205@pengutronix.de> <52DD0F72.1000005@pengutronix.de> <52DD1058.4090205@codethink.co.uk> In-Reply-To: <52DD1058.4090205@codethink.co.uk> To: Ben Dooks Cc: Geert Uytterhoeven , Sergei Shtylyov , "netdev@vger.kernel.org" , wg@grandegger.com, linux-can@vger.kernel.org, Linux-sh list , vksavl@gmail.com This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --JktNm4E6ofJADlcojgfVkjSBVD1glpcxU Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 01/20/2014 01:02 PM, Ben Dooks wrote: > On 20/01/14 11:58, Marc Kleine-Budde wrote: >> On 01/20/2014 12:52 PM, Geert Uytterhoeven wrote: >>> On Mon, Jan 20, 2014 at 12:47 PM, Marc Kleine-Budde >>> wrote: >>>> On 01/20/2014 12:43 PM, Geert Uytterhoeven wrote: >>>>> On Thu, Dec 26, 2013 at 10:37 PM, Sergei Shtylyov >>>>> wrote: >>>>>> Changes in version 3: >>>>> >>>>>> - added '__packed' to 'struct rcar_can_mbox_regs' and 'struct >>>>>> rcar_can_regs'; >>>>>> - removed unneeded type cast in the probe() method. >>>>> >>>>>> +/* Mailbox registers structure */ >>>>>> +struct rcar_can_mbox_regs { >>>>>> + u32 id; /* IDE and RTR bits, SID and EID */ >>>>>> + u8 stub; /* Not used */ >>>>>> + u8 dlc; /* Data Length Code - bits [0..3] */ >>>>>> + u8 data[8]; /* Data Bytes */ >>>>>> + u8 tsh; /* Time Stamp Higher Byte */ >>>>>> + u8 tsl; /* Time Stamp Lower Byte */ >>>>>> +} __packed; >>>>> >>>>> Sorry, I missed the earlier discussion, but why the _packed? >>>>> One u32 and 12 bytes makes a nice multiple of 4. >>>> >>>> Better safe than sorry, it's the layout of the registers in hardware= , >>>> don't let the compiler optimize here. >>> >>> Actually __packed makes it less safe, as the compiler now assumes >>> the u32 id member is unaligned, and thus may turn 32-bit accesses int= o 4 >>> byte accesses. >>> >>> Fortunately it won't happen in this case as the code uses >>> writel/readl to >>> acces the id member. >> >> Yes, as this are registers they must not be accessed directly. However= >> we can use "__attribute__ ((packed, aligned(4)))" to tell the compiler= >> that the base address of this struct is always aligned to 4 bytes. >=20 > I thought we'd gotten past the stage of ever writing register > definitions as structures? I don't care whether to use offsets defined by a #define or an enum or a struct. What's the "official" preference? Is it documented somewhere? Marc --=20 Pengutronix e.K. | Marc Kleine-Budde | Industrial Linux Solutions | Phone: +49-231-2826-924 | Vertretung West/Dortmund | Fax: +49-5121-206917-5555 | Amtsgericht Hildesheim, HRA 2686 | http://www.pengutronix.de | --JktNm4E6ofJADlcojgfVkjSBVD1glpcxU Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: Using GnuPG with Icedove - http://www.enigmail.net/ iEYEARECAAYFAlLdERcACgkQjTAFq1RaXHMXAQCglTPotRnqlwILrgzbd3rPSEzk /wgAnRQu2r87e8jCPhocgPBeOeL72sck =dl8e -----END PGP SIGNATURE----- --JktNm4E6ofJADlcojgfVkjSBVD1glpcxU-- From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marc Kleine-Budde Subject: Re: [PATCH v5] can: add Renesas R-Car CAN driver Date: Mon, 20 Jan 2014 13:05:43 +0100 Message-ID: <52DD1117.5030406@pengutronix.de> References: <201312270037.15822.sergei.shtylyov@cogentembedded.com> <52DD0CC1.70205@pengutronix.de> <52DD0F72.1000005@pengutronix.de> <52DD1058.4090205@codethink.co.uk> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="JktNm4E6ofJADlcojgfVkjSBVD1glpcxU" Return-path: Received: from metis.ext.pengutronix.de ([92.198.50.35]:54198 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751665AbaATMFv (ORCPT ); Mon, 20 Jan 2014 07:05:51 -0500 In-Reply-To: <52DD1058.4090205@codethink.co.uk> Sender: linux-can-owner@vger.kernel.org List-ID: To: Ben Dooks Cc: Geert Uytterhoeven , Sergei Shtylyov , "netdev@vger.kernel.org" , wg@grandegger.com, linux-can@vger.kernel.org, Linux-sh list , vksavl@gmail.com This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --JktNm4E6ofJADlcojgfVkjSBVD1glpcxU Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 01/20/2014 01:02 PM, Ben Dooks wrote: > On 20/01/14 11:58, Marc Kleine-Budde wrote: >> On 01/20/2014 12:52 PM, Geert Uytterhoeven wrote: >>> On Mon, Jan 20, 2014 at 12:47 PM, Marc Kleine-Budde >>> wrote: >>>> On 01/20/2014 12:43 PM, Geert Uytterhoeven wrote: >>>>> On Thu, Dec 26, 2013 at 10:37 PM, Sergei Shtylyov >>>>> wrote: >>>>>> Changes in version 3: >>>>> >>>>>> - added '__packed' to 'struct rcar_can_mbox_regs' and 'struct >>>>>> rcar_can_regs'; >>>>>> - removed unneeded type cast in the probe() method. >>>>> >>>>>> +/* Mailbox registers structure */ >>>>>> +struct rcar_can_mbox_regs { >>>>>> + u32 id; /* IDE and RTR bits, SID and EID */ >>>>>> + u8 stub; /* Not used */ >>>>>> + u8 dlc; /* Data Length Code - bits [0..3] */ >>>>>> + u8 data[8]; /* Data Bytes */ >>>>>> + u8 tsh; /* Time Stamp Higher Byte */ >>>>>> + u8 tsl; /* Time Stamp Lower Byte */ >>>>>> +} __packed; >>>>> >>>>> Sorry, I missed the earlier discussion, but why the _packed? >>>>> One u32 and 12 bytes makes a nice multiple of 4. >>>> >>>> Better safe than sorry, it's the layout of the registers in hardware= , >>>> don't let the compiler optimize here. >>> >>> Actually __packed makes it less safe, as the compiler now assumes >>> the u32 id member is unaligned, and thus may turn 32-bit accesses int= o 4 >>> byte accesses. >>> >>> Fortunately it won't happen in this case as the code uses >>> writel/readl to >>> acces the id member. >> >> Yes, as this are registers they must not be accessed directly. However= >> we can use "__attribute__ ((packed, aligned(4)))" to tell the compiler= >> that the base address of this struct is always aligned to 4 bytes. >=20 > I thought we'd gotten past the stage of ever writing register > definitions as structures? I don't care whether to use offsets defined by a #define or an enum or a struct. What's the "official" preference? Is it documented somewhere? Marc --=20 Pengutronix e.K. | Marc Kleine-Budde | Industrial Linux Solutions | Phone: +49-231-2826-924 | Vertretung West/Dortmund | Fax: +49-5121-206917-5555 | Amtsgericht Hildesheim, HRA 2686 | http://www.pengutronix.de | --JktNm4E6ofJADlcojgfVkjSBVD1glpcxU Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: Using GnuPG with Icedove - http://www.enigmail.net/ iEYEARECAAYFAlLdERcACgkQjTAFq1RaXHMXAQCglTPotRnqlwILrgzbd3rPSEzk /wgAnRQu2r87e8jCPhocgPBeOeL72sck =dl8e -----END PGP SIGNATURE----- --JktNm4E6ofJADlcojgfVkjSBVD1glpcxU--