[PATCH 08/11] drm/radeon/ci: apply disp voltage changes before clk changes

[Alex Deucher]

On Wed, Nov 19, 2014 at 4:59 PM, Alexandre Demers
<alexandre.f.demers at gmail.com> wrote:
> Technical reminder about this patch: usually, for electronic
> stability, you'll have to raise the voltage BEFORE increasing the
> clock speed; on the other, you'll have to lower the voltage AFTER
> lowering the clock speed. You may encounter stability problem if you
> don't follow this order.
>
> The patch fixes the first case, but you may end up creating the
> opposite problem by only moving
> ci_apply_disp_minimum_voltage_request(rdev) earlier in the process.
> But it may actually be covered by ci_send_msg_to_smc_with_parameter()
> or it may not be actually what ci_upload_dpm_level_enable_mask() is
> about.
>
> Is this patch linked to a specific bug?

There's no specific bug and the smc actually changes the voltages and
clocks internally in firmware so the driver doesn't really have to
worry about that.  This specific function just tells the smc to set a
new voltage floor based on potentially new requirements from the
display hw.  I don't know of any specific problems, it's just the
current recommended order from the power teams.

Alex