[Bug 1941622] Re: Bump unmatched CPU clock rate to 1.5GHz

[Heinrich Schuchardt]

The CPU clock rate is currently set in U-Boot SPL. SiFive said that
there are boards that are unstable over 1.2 GHz. So raising to 1.5 GHz
is not an option.

Currently the shut of temperature of the CPU is 108 °C. In the SiFive
repo there is a patch for lowering this to 85°C. I would advise not to
change the clock speed via the U-Boot dtb without adjusting the CPU
temperature limit too.

$ sensors # from lm-sensors package
tmp451-i2c-0-4c
Adapter: i2c-ocores
M/B Temp:     +46.1°C  (low  =  +0.0°C, high = +85.0°C)
                       (crit = +85.0°C, hyst = +75.0°C)
CPU Temp:     +48.2°C  (low  =  +0.0°C, high = +85.0°C)
                       (crit = +108.0°C, hyst = +98.0°C)

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https://bugs.launchpad.net/bugs/1941622

Title:
  Bump unmatched CPU clock rate to 1.5GHz

Status in u-boot package in Ubuntu:
  New

Bug description:
  [Impact]

  Bump unmatched CPU clock rate to 1.5GHz

  Multiple users report that running unmatched at 1.5GHz is stable, and
  gives one performance.

  Lets bump clock speed to 1.5GHz in u-boot and kernel.

  [Test Plan]

   * System with these patches boots, operates normally without
  overheating. CPU clock speed is increased to 1.5GHz.

  [Where problems could occur]

   * Overheating, instability, panics.

  [Other Info]
   
   * wgrant & multiple forum users report this configuration to be stable

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