From: Viresh Kumar <viresh.kumar@linaro.org>
To: Akhil P Oommen <akhilpo@codeaurora.org>
Cc: Nishanth Menon <nm@ti.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
linux-pm@vger.kernel.org, Stephen Boyd <sboyd@kernel.org>,
Viresh Kumar <vireshk@kernel.org>,
Rafael Wysocki <rjw@rjwysocki.net>,
linux-kernel@vger.kernel.org, Sibi Sankar <sibis@codeaurora.org>,
Dmitry Osipenko <digetx@gmail.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 03/13] opp: Keep track of currently programmed OPP
Date: Thu, 28 Jan 2021 09:44:31 +0530 [thread overview]
Message-ID: <20210128041431.rnfp3yrh7mp7e2gb@vireshk-i7> (raw)
In-Reply-To: <d9808e5f-bb8e-0d5c-8432-d695f8049f85@codeaurora.org>
On 27-01-21, 22:01, Akhil P Oommen wrote:
> On 1/22/2021 10:15 AM, Viresh Kumar wrote:
> > 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.
> >
> 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.
I see. I will make the necessary changes then to fix it. Thanks guys.
--
viresh
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next prev parent reply other threads:[~2021-01-28 4:15 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-21 11:17 [PATCH 00/13] opp: Implement dev_pm_opp_set_opp() Viresh Kumar
2021-01-21 11:17 ` [PATCH 01/13] opp: Rename _opp_set_rate_zero() Viresh Kumar
2021-01-21 11:17 ` [PATCH 02/13] opp: No need to check clk for errors Viresh Kumar
2021-01-21 11:17 ` [PATCH 03/13] opp: Keep track of currently programmed OPP Viresh Kumar
2021-01-21 21:41 ` Dmitry Osipenko
2021-01-22 4:45 ` Viresh Kumar
2021-01-22 14:31 ` Dmitry Osipenko
2021-01-25 3:12 ` Viresh Kumar
[not found] ` <d9808e5f-bb8e-0d5c-8432-d695f8049f85@codeaurora.org>
2021-01-28 4:14 ` Viresh Kumar [this message]
2021-07-07 10:24 ` Ionela Voinescu
2021-07-08 7:53 ` Viresh Kumar
2021-07-09 8:57 ` Ionela Voinescu
2021-07-12 4:14 ` Viresh Kumar
2021-01-21 11:17 ` [PATCH 04/13] opp: Split _set_opp() out of dev_pm_opp_set_rate() Viresh Kumar
2021-01-21 11:17 ` [PATCH 05/13] opp: Allow _set_opp() to work for non-freq devices Viresh Kumar
2021-01-21 11:17 ` [PATCH 06/13] opp: Allow _generic_set_opp_regulator() " Viresh Kumar
2021-01-21 11:17 ` [PATCH 07/13] opp: Allow _generic_set_opp_clk_only() " Viresh Kumar
2021-01-21 20:26 ` Dmitry Osipenko
2021-01-22 4:35 ` Viresh Kumar
2021-01-25 21:09 ` Dmitry Osipenko
2021-01-27 6:58 ` Viresh Kumar
2021-01-21 11:17 ` [PATCH 08/13] opp: Update parameters of _set_opp_custom() Viresh Kumar
2021-01-21 11:17 ` [PATCH 09/13] opp: Implement dev_pm_opp_set_opp() Viresh Kumar
2021-01-21 11:17 ` [PATCH 10/13] cpufreq: qcom: Migrate to dev_pm_opp_set_opp() Viresh Kumar
2021-01-21 11:17 ` [PATCH 11/13] devfreq: tegra30: " Viresh Kumar
2021-01-21 21:36 ` Dmitry Osipenko
2021-01-22 6:26 ` Viresh Kumar
2021-01-22 15:28 ` Dmitry Osipenko
2021-01-25 3:14 ` Viresh Kumar
2021-01-25 16:00 ` Dmitry Osipenko
2021-01-21 11:17 ` [PATCH 12/13] drm: msm: " Viresh Kumar
2021-01-21 11:17 ` [PATCH 13/13] opp: Remove dev_pm_opp_set_bw() Viresh Kumar
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