topic Re: Kernel logging causes USB instability in i.MX Processors

Kernel logging causes USB instability

dogisfat — Fri, 18 Jan 2019 23:58:43 GMT

We have a handful of kernel modules that can log a fair amount of data to the kernel logs. We have noticed that this can cause instability of the USB Camera we have plugged in. So far we have been struggling to come up with ideas on why kernel logging would cause this and possible remedy action besides reducing the amount of kernel logging.

Some ideas so far (keep in mind these may be very ignorant):

Kernel logging maybe gets written to disk and that freezes the system? Maybe DMA for the SD card takes over the memory bus and causes issues?

Kernel logging is higher priority than USB driver maintenance?

Any additional ideas or experiments would be appreciated.

Re: Kernel logging causes USB instability

igorpadykov — Tue, 22 Jan 2019 00:07:44 GMT

Hi ALLEN

in general logging (seems handled by uart) consumes some processor

time, internal buses and memory bandwidth which may affect usb module

operations. One can try to disable uart dma, use polling option. Another very general

way is to increase usb module priority with NIC-301 settings (sect.4.6 Network

Interconnect Bus System (NIC-301) i.MX7D Reference Manual), similar to

sect.45.3.3.1 QoS registers' address look-up example, sect.45.3.4 NIC-specific parameters

i.MX6DQ Reference Manual.

http://www.nxp.com/docs/en/reference-manual/IMX6DQRM.pdf

Unfortunately for i.MX7 such detailed NIC-301 description is not available.

Best regards
igor
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Re: Kernel logging causes USB instability

dogisfat — Wed, 06 Feb 2019 16:34:26 GMT

Is it possible to get a description of the NIC parameters and locations as in table 45-5 of the IMX6DQRM? Without that it is impossible to guess at the location and offset of the NIC configuration registers. We are also experiencing some issues with the M4 accessing DDR memory during high USB and Ethernet usage and would like to explore the NIC qos as a potential solution for that as well.

Re: Kernel logging causes USB instability

igorpadykov — Thu, 07 Feb 2019 00:39:44 GMT

for i.MX7 such detailed NIC-301 description is not available for customers,

suggest to work with nxp local marketing office if you have special need for it.

Best regards
igor