FSL serial 166550 errata broken?

[York Sun]

On 09/27/2017 04:03 AM, Joakim Tjernlund wrote:
> On Mon, 2017-09-25 at 17:26 +0000, York Sun wrote:
>> On 09/25/2017 09:55 AM, Joakim Tjernlund wrote:
>>> We got some "broken" boards(mpx8321) where UART RX is held low(BREAK)
>>> There we get a few:
>>>     serial8250: too much work for irq18
>>> and the board freezes.
>>>
>>> Looking inte to driver/CPU there is an errtum(A-004737) w.r.t BREAK handling
>>> and I can see we are hitting the irq function fsl8250_handle_irq() added
>>> in commit: 9deaa53ac7fa373623123aa4f18828dd62292b1a
>>>    "serial: add irq handler for Freescale 16550 errata."
>>> For all I can tell this workaround is broken and I cannot figure out why.
>>> Any pointers?
>>>
>>
>> Jocke,
>>
>> Did you mean MPC8321?
>>
>> I personally don't have experience debugging this erratum. Have you
>> tried to contact the patch author Paul Gortmaker to see how he managed
>> to get it work?
> 
> No, but I just found out it is u-boot related. If I use an very old u-boot it works.
> Between then and now we did a massive upgrade of u-boot and now if breaks. And no,
> bisect not possible due to local u-boot mods :)

How old? It is a good sign that an old U-Boot works. Git bisect would be 
a good tool if practical. Sometimes I have to reapply some local changes 
for every step of bisect to make it useful. You mileage may vary though.

> 
> Any idea what could be different? I cannot see and I have tested
> what I could see/think of but now I am out of ideas.

I don't believe we have much change for MPC8321 for a long time. If any 
change has impact on kernel but not U-Boot itself, it may be other 
errata workarounds.

I presume this happens on your own board. If I am in your shoes, I would 
try to reduce the number of local commits and reapply them to various 
U-Boot tags to further narrow down the search scope. In the mean time, 
getting register dump to compare the good and bad may be another way to go.

York