netdev - Re: [PATCH v5] can: add Renesas R-Car CAN driver

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Message-ID: <52DD0CC1.70205@pengutronix.de>
Date:	Mon, 20 Jan 2014 12:47:13 +0100
From:	Marc Kleine-Budde <mkl@...gutronix.de>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	wg@...ndegger.com, linux-can@...r.kernel.org,
	Linux-sh list <linux-sh@...r.kernel.org>, vksavl@...il.com
Subject: Re: [PATCH v5] can: add Renesas R-Car CAN driver

On 01/20/2014 12:43 PM, Geert Uytterhoeven wrote:
> Hi Sergei,
> 
> On Thu, Dec 26, 2013 at 10:37 PM, Sergei Shtylyov
> <sergei.shtylyov@...entembedded.com> 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.

Marc

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