UART RX losing bytes

UART RX losing bytes

[Gerz Burak LCPF-CH]

Hello,

v6.1.14 on a Phytec phyBoard Segin i.MX 6ULL based board [0] is losing bytes on UART RX.
imx_v6_v7_defconfig was used.

Minimalistic test to reproduce the issue:

1) Connect imx6ull UART with another machine
2) imx6ull$ stty -F /dev/ttymxc0 115200 raw; cat /dev/ttymcx0
3) othermachine$ stty -F /dev/USB0 115200 raw; 
    echo "1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$%-.,()/&" > /dev/ttyUSB0

Expected result:
imx6ull: 1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$%-.,()/&

Seen result (Many times, not always):
imx6ull: 1234567890abcdefghijklmnopqrstuvABCDEFGHIJKLMNOPQRSTUVWXYZ$%-.,()/&
or
imx6ull: 1234567890abcdefghijklmnopqrstuvBCDEFGHIJKLMNOPQRSTUVWXYZ$%-.,()/&
or
...

Setting scaling_governor to performance seems to be a workaround for this problem - but:
We are normally using the PREMPT_RT patch [1], and with this workaround bytes will still be lost

Any hints how to track this down further?

[0] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/arch/arm/boot/dts/imx6ull-phytec-segin-ff-rdk-nand.dts?h=v6.1.14 
[1] https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/tag/?h=v6.1.12-rt7

Re: UART RX losing bytes

[Sergey Organov]

Hello,

It reminds me about this:

https://marc.info/?l=linux-serial&m=166479501704202&w=2

HTH,
-- Sergey

Gerz Burak LCPF-CH <Burak.Gerz@mt.com> writes:

> Hello,
>
> v6.1.14 on a Phytec phyBoard Segin i.MX 6ULL based board [0] is losing bytes on UART RX.
> imx_v6_v7_defconfig was used.
>
> Minimalistic test to reproduce the issue:
>
> 1) Connect imx6ull UART with another machine
> 2) imx6ull$ stty -F /dev/ttymxc0 115200 raw; cat /dev/ttymcx0
> 3) othermachine$ stty -F /dev/USB0 115200 raw; 
>     echo "1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$%-.,()/&" > /dev/ttyUSB0
>
> Expected result:
> imx6ull: 1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$%-.,()/&
>
> Seen result (Many times, not always):
> imx6ull: 1234567890abcdefghijklmnopqrstuvABCDEFGHIJKLMNOPQRSTUVWXYZ$%-.,()/&
> or
> imx6ull: 1234567890abcdefghijklmnopqrstuvBCDEFGHIJKLMNOPQRSTUVWXYZ$%-.,()/&
> or
> ...
>
> Setting scaling_governor to performance seems to be a workaround for this problem - but:
> We are normally using the PREMPT_RT patch [1], and with this workaround bytes will still be lost
>
> Any hints how to track this down further?
>
> [0] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/arch/arm/boot/dts/imx6ull-phytec-segin-ff-rdk-nand.dts?h=v6.1.14 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/tag/?h=v6.1.12-rt7