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Message-ID: <5458D494.3040700@pengutronix.de>
Date: Tue, 04 Nov 2014 14:28:52 +0100
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: Oliver Hartkopp <socketcan@...tkopp.net>,
Dong Aisheng <b29396@...escale.com>
CC: linux-can@...r.kernel.org, wg@...ndegger.com,
varkabhadram@...il.com, netdev@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 7/7] can: m_can: workaround for transmit data less than
4 bytes
On 11/04/2014 02:13 PM, Oliver Hartkopp wrote:
>
>
> On 04.11.2014 11:33, Marc Kleine-Budde wrote:
>> On 11/04/2014 10:27 AM, Dong Aisheng wrote:
>
>
>>> + /* We meet an IC issue that we have to write the full 8
>>
>> At least on the *insert SoC name here*, an issue with the Message RAM
>> was discovered. Sending CAN frames with dlc less than 4 bytes will lead
>> to bit errors, when the first 8 bytes of the Message RAM have not been
>> initialized (i.e. written to). To work around this issue, the first 8
>> bytes are initialized here.
>
> Yes. Also put the current IP revision (3.0.x) into the comment.
Good idea - also add the SoC's mask revision.
> Did inform the Bosch guys from this issue - or is it already in some
> errata sheet?
>
>>
>>> + * bytes (whatever value for the second word) in Message RAM to
>>> + * avoid bit error for transmit data less than 4 bytes at the
>>> first
>>> + * time. By initializing the first 8 bytes of tx buffer
>>> before using
>>> + * it can avoid such issue.
>>> + */
>>> + m_can_fifo_write(priv, 0, M_CAN_FIFO_DATA(0), 0x0);
>>> + m_can_fifo_write(priv, 0, M_CAN_FIFO_DATA(1), 0x0);
>>> +
>>> m_can_config_endisable(priv, false);
>>> }
>>
>> Can you trigger the issue when sending CAN-FD frames with dlc > 8 && dlc
>> < 64?
>
> Just a nitpick:
>
> DLC can just be 0 .. 15
Correct, I was talking about the length
> and the length (struct canfd_frame.len) can be from 0 .. 64
>
> See:
>
> http://lxr.free-electrons.com/source/include/uapi/linux/can.h#L83
>
> That's the reason for all these helpers
>
> http://lxr.free-electrons.com/source/drivers/net/can/dev.c#L36
>
> that hide the evil "DLC" from userspace now and make 'len' a usable loop
> variable as we were able to use the former dlc for classic CAN :-)
Marc
--
Pengutronix e.K. | Marc Kleine-Budde |
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