[Bug 82781] Option to disable mclk reclocking with AMD R9 280X (TAHITI) to avoid screen flickering on VGA/CRT

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=82781

--- Comment #11 from Christian Birchinger <joker@netswarm.net> ---
Simply doing this also works:

ni_dpm.c:

bool ni_dpm_vblank_too_short(struct radeon_device *rdev)
{
  struct rv7xx_power_info *pi = rv770_get_pi(rdev);
  u32 vblank_time = r600_dpm_get_vblank_time(rdev);
  /* we never hit the non-gddr5 limit so disable it */
  u32 switch_limit = pi->mem_gddr5 ? 450 : 0;

  return true;

Adding a hardcoded true also disables mclk changes. which only leads
to one conclusion:

  if (vblank_time <= switch_limit)
    return true;
  else
    return false;

Somehow the values are not always 450 but i cannot see such a case
in the printk debug.

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