linux-kernel - Re: [PATCH v4 3/4] can: kvaser_usb: Add support for the Usbcan-II family

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Message-ID: <54BC1405.8010207@pengutronix.de>
Date:	Sun, 18 Jan 2015 21:13:57 +0100
From:	Marc Kleine-Budde <mkl@...gutronix.de>
To:	"Ahmed S. Darwish" <darwish.07@...il.com>,
	Olivier Sobrie <olivier@...rie.be>
CC:	Oliver Hartkopp <socketcan@...tkopp.net>,
	Wolfgang Grandegger <wg@...ndegger.com>,
	"David S. Miller" <davem@...emloft.net>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Linux-CAN <linux-can@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/4] can: kvaser_usb: Add support for the Usbcan-II
 family

On 01/18/2015 09:12 PM, Ahmed S. Darwish wrote:
> Hi!
> 
> On Mon, Jan 12, 2015 at 02:53:02PM +0100, Olivier Sobrie wrote:
>> Hello,
>>
>> On Sun, Jan 11, 2015 at 03:36:12PM -0500, Ahmed S. Darwish wrote:
>>> From: Ahmed S. Darwish <ahmed.darwish@...eo.com>
>>>
> 
> ...
> 
>>> @@ -98,7 +128,13 @@
>>>  #define CMD_START_CHIP_REPLY		27
>>>  #define CMD_STOP_CHIP			28
>>>  #define CMD_STOP_CHIP_REPLY		29
>>> -#define CMD_GET_CARD_INFO2		32
>>> +#define CMD_READ_CLOCK			30
>>> +#define CMD_READ_CLOCK_REPLY		31
>>
>> These two defines are not used.
>>
> 
> They were added for completeness: the only gap in our continuous
> sequence of command IDs from 12 to 39 ;-) No big deal, to be
> removed in the next submission.
> 
> ...
> 
>>> +
>>> +struct kvaser_msg_tx_acknowledge_header {
>>> +	u8 channel;
>>> +	u8 tid;
>>> +};
>>
>> Is this struct really needed? Can't you simply use
>> leaf_msg_tx_acknowledge or usbcan_msg_tx_acknowledge
>> structures to read the header.
>> Same for kvaser_msg_rx_can_header.
>>
> 
> They're added to ensure type-safety throughout the code. Basically
> they're the common part of a command that has different wire format
> between the Leaf and the USBCan, but share a common header.  Such
> notation was only added when it was strictly necessary.
> 
> For example, there are three functions where 'rx_can_header' is
> referenced in the driver, and one function where 'tx_acknowledge_header'
> is referenced. Without such header structure, I'll have to sprinkle
> 3 to 4 extra blocks of:
> 
> 	switch (dev->family) {
> 	       case KVASER_LEAF: 
> 	       case KVASER_USBCAN:
> 	}
> 
> which would be _really_ ugly. The *_header notation ensures that, in
> the body of each function, we're accessing the fields in a very safe
> manner.

+1 Keep it as it is.

Marc

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