[EXTERNAL]Re: FSL serial 166550 errata broken?

[Joakim Tjernlund]

On Thu, 2017-09-28 at 17:54 +0200, Joakim Tjernlund wrote:
> 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.
> 

Ok, unless I init ttyS1 in u-boot too, IRQ storm will ensue if BREAK is present
when opening ttyS1:
+       /* Must init the second RS232 or IRQ storm happens
+        * when BREAK is constant on while opening ttyS1 */
+       NS16550_init((NS16550_t)CONFIG_SYS_NS16550_COM2,
+                    ns16550_calc_divisor((NS16550_t)CONFIG_SYS_NS16550_COM2,
+                                         CONFIG_SYS_NS16550_CLK,
+                                         CONFIG_BAUDRATE));

I guess this is a kernel bug too, the driver should clear/init needed state before
starting the device. Fixing that is not on my menu though :)

I also noted that FSL custom irq handler, fsl8250_handle_irq, does not handle
dma like the standard one does. I guess it needs some love too.

 Jocke