On 1/22/2021 10:15 AM, Viresh Kumar wrote:

On 22-01-21, 00:41, Dmitry Osipenko wrote:

quoted

21.01.2021 14:17, Viresh Kumar пишет:

quoted

@@ -1074,15 +1091,18 @@ int dev_pm_opp_set_rate(struct device *dev, unsigned long target_freq)
  
  	if (!ret) {
  		ret = _set_opp_bw(opp_table, opp, dev, false);
-		if (!ret)
+		if (!ret) {
  			opp_table->enabled = true;
+			dev_pm_opp_put(old_opp);
+
+			/* Make sure current_opp doesn't get freed */
+			dev_pm_opp_get(opp);
+			opp_table->current_opp = opp;
+		}
  	}

I'm a bit surprised that _set_opp_bw() isn't used similarly to
_set_opp_voltage() in _generic_set_opp_regulator().

I'd expect the BW requirement to be raised before the clock rate goes UP.

I remember discussing that earlier when this stuff came in, and this I
believe is the reason for that.

We need to scale regulators before/after frequency because when we
increase the frequency a regulator may _not_ be providing enough power
to sustain that (even for a short while) and this may have undesired
effects on the hardware and so it is important to prevent that
malfunction.

In case of bandwidth such issues will not happen (AFAIK) and doing it
just once is normally enough. It is just about allowing more data to
be transmitted, and won't make the hardware behave badly.

I agree with Dmitry. BW is a shared resource in a lot of architectures. 
Raising clk before increasing the bw can lead to a scenario where this 
client saturate the entire BW for whatever small duration it may be. 
This will impact the latency requirements of other clients.

-Akhil.