[Buildroot] [Bug 9726] New: Raspberry Pi version B - Problems with UART speed in Buildroot 2016.11.2 and 2017.2

[Buildroot] [Bug 9726] New: Raspberry Pi version B - Problems with UART speed in Buildroot 2016.11.2 and 2017.2

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=9726

            Bug ID: 9726
           Summary: Raspberry Pi version B - Problems with UART speed in
                    Buildroot 2016.11.2 and 2017.2
           Product: buildroot
           Version: 2016.11
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P5
         Component: Other
          Assignee: unassigned at buildroot.uclibc.org
          Reporter: wzab01 at gmail.com
                CC: buildroot at uclibc.org
  Target Milestone: ---

We have a lab equipped with old Respberry Pi version B.
To allow student to modify the system image without removing and inserting SD
cards (which killed them in a few weeks), we use U-Boot bootloder, patched so
that it passes the boot parameters prepared via a standard RPi firmware.
I wanted to update our environment to Buildroot 2016.11.2 in this semester.
Unfortunately, it appears, that the U-Boot does not set the UART speed properly
in that scenario.
I've meassured the UART speed with the oscilloscope, and it appeared, that it
is equal to ca. 1840 kb/s. However, the kernel uses the correct UART speed -
115.2 kb/s.
I've also tested the operation with the Buildroot 2017.2
In this case things are even more interesting. The U-Boot sets the UART speed
correctly to 115.2 kb/s, but hte kernel works at 921.6 kb/s
What can be the reason of the experienced problems?
Can I easily cure them with the settings done in the config.txt file?

TIA & Regards,
Wojtek

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[Buildroot] [Bug 9726] Raspberry Pi version B - Problems with UART speed in Buildroot 2016.11.2 and 2017.2

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=9726

--- Comment #1 from WZab <wzab01@gmail.com> ---
Created attachment 6951
  --> https://bugs.busybox.net/attachment.cgi?id=6951&action=edit
Buildroot configuration to generate the U-Boot

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[Buildroot] [Bug 9726] Raspberry Pi version B - Problems with UART speed in Buildroot 2016.11.2 and 2017.2

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=9726

--- Comment #2 from WZab <wzab01@gmail.com> ---
I have fond the temporary workaround. The U-Boot generated with Buildroot
1016.02 and the attached configuration is able to load correctly the kernels
generated with 2016.11.
The zImage generated with the same configuration is used as a "rescue image"
allowing to modify the contents of the SD card without removing it.

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[Buildroot] [Bug 9726] Raspberry Pi version B - Problems with UART speed in Buildroot 2016.11.2 and 2017.2

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=9726

Thomas Petazzoni <thomas.petazzoni@free-electrons.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |WORKSFORME
             Status|NEW                         |RESOLVED

--- Comment #3 from Thomas Petazzoni <thomas.petazzoni@free-electrons.com> ---
Thanks for reporting this bug. However, this doesn't look like a Buildroot
problem, but more a U-Boot or Linux kernel problem. That being said, tons of
people are using our RPi defconfigs, and they seem to work fine, you are the
only one to report such issues.

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[Buildroot] [Bug 9726] Raspberry Pi version B - Problems with UART speed in Buildroot 2016.11.2 and 2017.2

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=9726

--- Comment #4 from WZab <wzab01@gmail.com> ---
I agree, that defconfigs work correctly, because they do not use U-Boot.
Probably this is a U-Boot related problem.
At the moment we are using the U-Boot from BR 2016.02, which works fine.
If I'll find any explanation of the problem and a fix, I'll report it

With best regards,
Wojtek

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