Messages in this thread | | | Date | Fri, 22 Jan 2021 10:15:32 +0530 | From | Viresh Kumar <> | Subject | Re: [PATCH 03/13] opp: Keep track of currently programmed OPP |
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On 22-01-21, 00:41, Dmitry Osipenko wrote: > 21.01.2021 14:17, Viresh Kumar пишет: > > @@ -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.
-- viresh
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