On Thu, Feb 4, 2016 at 10:06 PM, Peter Hurley [off-list ref] wrote:

Hi Andy,

On 02/04/2016 10:55 AM, Andy Shevchenko wrote:

quoted

Hi!

Today I observed interesting bug / feature of uart layer in the kernel.
I do have a setup which connects two identical devices by serial line.
I run data transferring in one direction and got data corruption on
receiver side (in uart layer, not the driver).

Here is the dump from test suite and real data from 8250 registers:

=== 8< ===

Needed 16 reads 0 writes Oh oh, inconsistency at pos 1 (0x1).

Original sample:
00000000: 7f 45 4c 46 01 01 01 00  00 00 00 00 00 00 00 00   .ELF............
00000010: 02 00 03 00 01 00 00 00  19 8d 04 08 34 00 00 00   ............4...
00000020: 2c f2 00 00 00 00 00 00  34 00 20 00 04 00 28 00   ,.......4. ...(.

Received sample:
00000000: 7f 00 45 00 4c 00 46 00  01 00 01 00 01 00 00 00   ..E.L.F.........
00000010: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00   ................
00000020: 02 00 00 00 03 00 00 00  01 00 00 00 00 19 8d 04   ................
loops 1 / 1

cts: 0 dsr: 0 rng: 0 dcd: 0 rx: 53434 tx: 0 frame 0 ovr 34201 par: 0
brk: 0 buf_ovrr: 0

=== 8< ===

R 356.360109 IIR 0xc4           RDI interrupt
R 356.360114 LSR 0x63           DR + OE
R 356.360119 RX 0x7f
R 356.360124 LSR 0x63           DR + still OE
R 356.360128 RX 0x45
R 356.360133 LSR 0x63           DR + still OE
R 356.360137 RX 0x4c
R 356.360142 LSR 0x63           DR + still OE
R 356.360147 RX 0x46
R 356.360151 LSR 0x63           DR + still OE
R 356.360156 RX 0x01
R 356.360160 LSR 0x63           DR + still OE
R 356.360165 RX 0x01
R 356.360169 LSR 0x63
R 356.360174 RX 0x01

As we can see the data is corrupted on Linux side. Can we somehow fix
this bug/feature?

Not quite sure what you see as the issue.

1) That is a lot of overruns. Is that part of the test or are the overruns
   a regression?

This is part of the other problem which I'm investigating.

2) If you mean the NUL bytes for overruns, I could have some functional mode
   mis-branched in the N_TTY line discipline.

Yeah, this one.

What are the termios settings
   on the rx side?

I'm using this [1] tool with small patch applied that enables internal
loopback (TCIOM_LOOP).

[1] https://git.breakpoint.cc/cgit/bigeasy/serialcheck.git/

-- 
With Best Regards,
Andy Shevchenko