From: Oliver Hartkopp <socketcan@hartkopp.net>
To: Dong Aisheng <b29396@freescale.com>
Cc: Marc Kleine-Budde <mkl@pengutronix.de>,
linux-can@vger.kernel.org, wg@grandegger.com,
varkabhadram@gmail.com, netdev@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: M_CAN message RAM initialization AppNote - was: Re: [PATCH V3 3/3] can: m_can: workaround for transmit data less than 4 bytes
Date: Thu, 06 Nov 2014 13:33:56 +0100 [thread overview]
Message-ID: <545B6AB4.70003@hartkopp.net> (raw)
In-Reply-To: <20141106080940.GA22964@shlinux1.ap.freescale.net>
On 06.11.2014 09:09, Dong Aisheng wrote:
> On Thu, Nov 06, 2014 at 08:04:17AM +0100, Oliver Hartkopp wrote:
>> To prevent the M_CAN controller detecting checksum errors when
>> reading potentially uninitialized TX message RAM content to transmit
>> CAN frames the TX message RAM has to be written with (any kind of)
>> initial data.
>>
>
> The key point of the issue is that why M_CAN will read potentially uninitialized
> TX message RAM content which should not happen?
> e.g. for our case of the issue, if we sending a no data frame or a less
> than 4 bytes frame, why m_can will read extra 4 bytes uninitialized/unset
> data which seems not reasonable?
>
> From IP code logic, it will read full 8 bytes of data no matter how many data
> actually to be transfered which is strange.
Yes.
>
> For sending data over 4 bytes, since the Message RAM content will be filled
> with the real data to be transfered so there's no such issue.
E.g. think about the transfer of a CAN FD frame with 32 byte.
When you only fill up content until 28 byte the last four bytes still remain
uninitialized.
Did you try this 28 byte use-case with an uninitialized TX message RAM ?
cansend can0 123##1001122334566778899AABBCCDDEEFF001122334566778899AABB
To me it looks too risky when we only initialize the first 8 byte.
>
>> ---
>>
>> Then the code should memset() the entire TX FIFO element - and not
>> only the 8 data bytes we are addressing now.
>>
>
> Our IC guy told me the issue only happened on transferring a data size
> of less than 4 bytes and my test also proved that.
'less than'?
So you might try to use 26 bytes too:
cansend can0 123##1001122334566778899AABBCCDDEEFF001122334566778899
> So i'm not sure memset() the entire TX FIFO element is neccesary...
It's no big deal - so we should be defensive here.
And memset() is not working as Marc pointed out in another mail.
So we would need to loop with
m_can_fifo_write(priv, 0, M_CAN_FIFO_DATA(i), 0x0);
>
> Do you think we could keep the current solution firstly and updated later
> if needed?
No :-)
I would like to have all data bytes to be written at startup.
Regards,
Oliver
next prev parent reply other threads:[~2014-11-06 12:34 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-05 13:16 [PATCH V3 1/3] can: add can_is_canfd_skb() API Dong Aisheng
2014-11-05 13:16 ` [PATCH V3 2/3] can: m_can: update to support CAN FD features Dong Aisheng
2014-11-05 14:31 ` Marc Kleine-Budde
2014-11-05 14:42 ` Oliver Hartkopp
2014-11-05 13:16 ` [PATCH V3 3/3] can: m_can: workaround for transmit data less than 4 bytes Dong Aisheng
2014-11-05 14:29 ` Marc Kleine-Budde
2014-11-05 18:15 ` M_CAN message RAM initialization AppNote - was: " Oliver Hartkopp
2014-11-06 1:57 ` Dong Aisheng
2014-11-06 7:04 ` Oliver Hartkopp
2014-11-06 8:09 ` Dong Aisheng
2014-11-06 12:33 ` Oliver Hartkopp [this message]
2014-11-06 12:47 ` Marc Kleine-Budde
[not found] ` <545BA039.7080108@hartkopp.net>
2014-11-07 8:15 ` Dong Aisheng
2015-02-05 19:04 ` new M_CAN IP rev 3.2.x documentation available - was: Re: M_CAN message RAM initialization AppNote Oliver Hartkopp
2014-11-07 8:40 ` M_CAN message RAM initialization AppNote - was: Re: [PATCH V3 3/3] can: m_can: workaround for transmit data less than 4 bytes Dong Aisheng
2014-11-07 8:34 ` Dong Aisheng
2014-11-06 9:00 ` Marc Kleine-Budde
2014-11-05 16:22 ` [PATCH V3 1/3] can: add can_is_canfd_skb() API Eric Dumazet
2014-11-05 17:33 ` Oliver Hartkopp
2014-11-06 1:52 ` Dong Aisheng
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