netdev - Re: [PATCH V2] CAN: Add Flexcan CAN controller driver

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Message-ID: <4A6F546A.4000008@grandegger.com>
Date:	Tue, 28 Jul 2009 21:41:30 +0200
From:	Wolfgang Grandegger <wg@...ndegger.com>
To:	Sascha Hauer <s.hauer@...gutronix.de>
CC:	Oliver Hartkopp <socketcan@...tkopp.net>,
	Socketcan-core@...ts.berlios.de,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [PATCH V2] CAN: Add Flexcan CAN controller driver

Sascha Hauer wrote:
> On Tue, Jul 28, 2009 at 04:48:34PM +0200, Oliver Hartkopp wrote:
>> Sascha Hauer wrote:
>>> On Tue, Jul 28, 2009 at 04:12:10PM +0200, Oliver Hartkopp wrote:
>>>> Oliver Hartkopp wrote:
>>>>> Sascha Hauer wrote:
>>>>>>>> +
>>>>>>>> +	if (frame->can_id & CAN_RTR_FLAG)
>>>>>>>> +		dlc |= MB_CNT_RTR;
>>>>>>>> +
>>>>>>>> +	writel(dlc, &regs->cantxfg[TX_BUF_ID].can_dlc);
>>>>>>>> +	writel(can_id, &regs->cantxfg[TX_BUF_ID].can_id);
>>>> Are you sure, that this is correct?
>>> Yes, I am sure, at least on my hardware.
>> I looked into the writel() macro which does a cpu_to_le32() to the value -
>> sorry that i did not check this before ...
>>
>>>> Indeed i wonder, if it would make sense to skip the entire struct flexcan_mb
>>>> approach and fiddle byte-by-byte inside the registers ...
>>> You'll have to to 32 bit accesses to get it right on little and big
>>> endian.
>>>
>>> what we can do is:
>>>
>>> writel(can_data[0] << 24 | can_data[1] << 16 | can_data[2] << 8 | can_data[3],
>>> 	msg_buf + 0x8);
>> This looks easier to understand and makes things clear, when you look into the
>> specification.
> 
> Ok, I'll change it like this.

OK, even if I do not really share Oliver's concerns. The second write
could be suppressed if dlc <= 4.

Wolfgang.
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