[EXTERNAL]Re: FSL serial 166550 errata broken?

[Joakim Tjernlund]

On Wed, 2017-09-27 at 15:32 +0000, York Sun wrote:
> 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.

God, this was no fun exercise but I think I found the offending commit: 82dda962f0a6449672df3378bb6b5fe54372a927
    serial: Unconditionally enable CONFIG_SERIAL_MULTI
    
    Enable CONFIG_SERIAL_MULTI for all builds of U-Boot. That includes
    both SPL builds and non-SPL builds, everything. To avoid poluting
    this patch with removal of ifdef-endif constructions containing
    CONFIG_SERIAL_MULTI, the CONFIG_SERIAL_MULTI is temporarily added
    into CPPFLAGS in config.mk . This will be again removed in following
    patch.