From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marc Kleine-Budde Date: Mon, 20 Jan 2014 11:58:42 +0000 Subject: Re: [PATCH v5] can: add Renesas R-Car CAN driver Message-Id: <52DD0F72.1000005@pengutronix.de> MIME-Version: 1 Content-Type: multipart/mixed; boundary="kgDSoo8CwiBQwOnOPDfda7rFU0pXa6oCG" List-Id: References: <201312270037.15822.sergei.shtylyov@cogentembedded.com> <52DD0CC1.70205@pengutronix.de> In-Reply-To: To: Geert Uytterhoeven Cc: 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) --kgDSoo8CwiBQwOnOPDfda7rFU0pXa6oCG Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable 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_c= an_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. >=20 > Actually __packed makes it less safe, as the compiler now assumes > the u32 id member is unaligned, and thus may turn 32-bit accesses into = 4 > byte accesses. >=20 > 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. 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 | --kgDSoo8CwiBQwOnOPDfda7rFU0pXa6oCG 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/ iEYEARECAAYFAlLdD3IACgkQjTAFq1RaXHPk5gCgh0O/Wc8bVK+ye3hF/vX1a15k edUAoIRfxWip/fvVOWsdykUirarksgkr =2cWM -----END PGP SIGNATURE----- --kgDSoo8CwiBQwOnOPDfda7rFU0pXa6oCG-- 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 12:58:42 +0100 Message-ID: <52DD0F72.1000005@pengutronix.de> References: <201312270037.15822.sergei.shtylyov@cogentembedded.com> <52DD0CC1.70205@pengutronix.de> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="kgDSoo8CwiBQwOnOPDfda7rFU0pXa6oCG" Return-path: Received: from metis.ext.pengutronix.de ([92.198.50.35]:43631 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750822AbaATL6w (ORCPT ); Mon, 20 Jan 2014 06:58:52 -0500 In-Reply-To: Sender: linux-can-owner@vger.kernel.org List-ID: To: Geert Uytterhoeven Cc: 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) --kgDSoo8CwiBQwOnOPDfda7rFU0pXa6oCG Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable 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_c= an_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. >=20 > Actually __packed makes it less safe, as the compiler now assumes > the u32 id member is unaligned, and thus may turn 32-bit accesses into = 4 > byte accesses. >=20 > 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. 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 | --kgDSoo8CwiBQwOnOPDfda7rFU0pXa6oCG 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/ iEYEARECAAYFAlLdD3IACgkQjTAFq1RaXHPk5gCgh0O/Wc8bVK+ye3hF/vX1a15k edUAoIRfxWip/fvVOWsdykUirarksgkr =2cWM -----END PGP SIGNATURE----- --kgDSoo8CwiBQwOnOPDfda7rFU0pXa6oCG--