[Bug 111482] Sapphire Pulse RX 5700 XT power consumption

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111482

--- Comment #23 from Andrew Sheldon <asheldon55 at gmail.com> ---
@Leon

I suspect there is more than one bug occurring. The main Navi-specific issue
has been fixed with newer kernels (that affected everyone), but there is
another issue relating to high resolution and high refresh rate monitors, that
looks to affect at least Navi, Vega (and probably Polaris going by other
reports).

The secondary issue is probably by design to an extent. High res/refresh rate
requires a lot more bandwidth which needs a higher memory clock. However, I
suspect there are two problems within this:

- Once a high bandwidth mode is used and the maximum memory clock is chosen, it
never switches down again (even if you switch to a lower bandwidth mode).
Particularly, if you boot at 2560x1440 at 144hz, you won't be able to switch down
again.
- The choice of memory clock is higher than it needs to be, even for high
bandwidth modes

You can workaround this to some extent on Vega by writing to the powerplay
tables (while in a high bandwidth mode) and, in the case of Vega, the card will
stay in the more reasonable memory clock of 700mhz (versus the max of 950mhz).
However, if you then switch to any other high bandwidth mode (e.g.
2560x1440 at 120), the problem will return (card stuck at 950mhz).

I don't recommend trying that on Navi as powerplay table writing is currently
buggy without reverting a commit, I haven't confirmed the behaviour there, but
I suspect the same workaround will work.

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