imprecise external abort using the flexcan driver on i.MX6Q

[mkl@pengutronix.de (Marc Kleine-Budde)]

On 09/30/2013 01:06 PM, Lothar Wa?mann wrote:
> Hi,
> 
> Marc Kleine-Budde writes:
>> On 09/27/2013 07:24 PM, Matt Sealey wrote:
>>> Marc - I don't think FLEXCAN has changed layout at all in these areas.
>>> The hardware always worked this way..
>>
>> All flexcan cores support the RX FIFO, the mx6 supports an additional
>> mode for different acceptance filters.
>>
>>> The only difference here  is that the i.MX53 is doing something weird
>>> on the bus. The i.MX6Q is giving the absolutely correct BRESP for the
>>> transfer to the peripheral (in effect, a "go away, this is my data"
>>> failure, which the CPU turns into an imprecise abort since it no idea
>>> which transaction it committed aeons ago caused it).
>>>
>>> Writes to 0x90 to 0xDF while MCR[FEN] is set *should* cause a data
>>> abort.. because it's not even a read-only region, it *should* be
>>> totally inaccessible to the CPU.
>>>
>>> The question I have is, when MCR[FEN] is set on i.MX53, does reading
>>> from those reserved registers give anything but 0's or garbage? I'm
>>> curious, that's all, it doesn't really matter ;)
>>
>> The driver only read from message buffer 0, and uses buffer 8 for tx.
>> The others are not accessed, unless in that chip start routine. We don't
>> need this loop, it comes from the original driver. I think no one has
>> ever noticed that bug, because all other CPUs have not complained.
>>
>> The driver without the loop is working on mx6 and Lothar is testing it
>> on mx53.
>>
> I can confirm, that the driver still works on i.MX53 as before the
> patch.
> Is someone going to prepare a patch, or should I do it, as I was the
> one who first brought up this issue?

I have a patch ready, it's basically what I send you. Can I add your
Tested-by?

Marc

-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
Industrial Linux Solutions        | Phone: +49-231-2826-924     |
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