Re: imprecise external abort using the flexcan driver on i.MX6Q

["Lothar Waßmann" <LW@KARO-electronics.de>]

Hi,

Marc Kleine-Budde writes:
> On 09/30/2013 01:06 PM, Lothar Waßmann 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?
> 
Yes, of course.


Lothar Waßmann
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