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The original CPU voltage value for load L1 is too low for Armada 37xx SoC when base CPU frequency is 1000 or 1200 MHz. It leads to instabilities where CPU gets stuck soon after dynamic voltage scaling from load L1 to L0. Update the CPU voltage value for load L1 accordingly when base frequency is 1000 or 1200 MHz. The minimal L1 value for base CPU frequency 1000 MHz is updated from the original 1.05V to 1.108V and for 1200 MHz is updated to 1.155V. This minimal L1 value is used only in the case when it is lower than value for L0. This change fixes CPU instability issues on 1 GHz and 1.2 GHz variants of Espressobin and 1 GHz Turris Mox. Marvell previously for 1 GHz variant of Espressobin provided a patch [1] suitable only for their Marvell Linux kernel 4.4 fork which workarounded this issue. Patch forced CPU voltage value to 1.108V in all loads. But such change does not fix CPU instability issues on 1.2 GHz variants of Armada 3720 SoC. During testing we come to the conclusion that using 1.108V as minimal value for L1 load makes 1 GHz variants of Espressobin and Turris Mox boards stable. And similarly 1.155V for 1.2 GHz variant of Espressobin. These two values 1.108V and 1.155V are documented in Armada 3700 Hardware Specifications as typical initial CPU voltage values. Discussion about this issue is also at the Armbian forum [2]. [1] - |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.