Re: [EXTERNAL]Re: FSL serial 166550 errata broken?

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

On 09/27/2017 04:03 AM, Joakim Tjernlund wrote:

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On Mon, 2017-09-25 at 17:26 +0000, York Sun wrote:

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On 09/25/2017 09:55 AM, Joakim Tjernlund wrote:

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We got some "broken" boards(mpx8321) where UART RX is held low(BREA=

K)

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There we get a few:
    serial8250: too much work for irq18
and the board freezes.
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Looking inte to driver/CPU there is an errtum(A-004737) w.r.t BREAK=

 handling

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and I can see we are hitting the irq function fsl8250_handle_irq() =

added

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in commit: 9deaa53ac7fa373623123aa4f18828dd62292b1a
   "serial: add irq handler for Freescale 16550 errata."
For all I can tell this workaround is broken and I cannot figure ou=

t why.

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Any pointers?
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Jocke,
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Did you mean MPC8321?
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I personally don't have experience debugging this erratum. Have you
tried to contact the patch author Paul Gortmaker to see how he manage=

d

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to get it work?

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No, but I just found out it is u-boot related. If I use an very old u-b=

oot it works.

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Between then and now we did a massive upgrade of u-boot and now if brea=

ks. And no,

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bisect not possible due to local u-boot mods :)

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How old? It is a good sign that an old U-Boot works. Git bisect would be=

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a good tool if practical. Sometimes I have to reapply some local changes=

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for every step of bisect to make it useful. You mileage may vary though.
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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.

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I don't believe we have much change for MPC8321 for a long time. If any=20
change has impact on kernel but not U-Boot itself, it may be other=20
errata workarounds.
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I presume this happens on your own board. If I am in your shoes, I would=

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try to reduce the number of local commits and reapply them to various=20
U-Boot tags to further narrow down the search scope. In the mean time,=20
getting register dump to compare the good and bad may be another way to g=

o.

God, this was no fun exercise but I think I found the offending commit: 82d=
da962f0a6449672df3378bb6b5fe54372a927
    serial: Unconditionally enable CONFIG_SERIAL_MULTI
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    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.