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From: Akhil P Oommen <akhilpo@codeaurora.org>
To: Viresh Kumar <viresh.kumar@linaro.org>,
	Dmitry Osipenko <digetx@gmail.com>
Cc: Viresh Kumar <vireshk@kernel.org>, Nishanth Menon <nm@ti.com>,
	Stephen Boyd <sboyd@kernel.org>,
	linux-pm@vger.kernel.org,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Rafael Wysocki <rjw@rjwysocki.net>,
	Sibi Sankar <sibis@codeaurora.org>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 03/13] opp: Keep track of currently programmed OPP
Date: Wed, 27 Jan 2021 22:01:03 +0530	[thread overview]
Message-ID: <d9808e5f-bb8e-0d5c-8432-d695f8049f85@codeaurora.org> (raw)
In-Reply-To: <20210122044532.pc7cpcgy3kjbqmls@vireshk-i7>

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.

-Akhil.

  parent reply	other threads:[~2021-01-27 16:33 UTC|newest]

Thread overview: 39+ 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
2021-01-27 16:31       ` Akhil P Oommen [this message]
2021-01-28  4:14         ` Viresh Kumar
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
2021-01-27  9:10   ` [PATCH V2 " Viresh Kumar
2021-01-27 10:02     ` Viresh Kumar
2021-01-27 15:58       ` Dmitry Osipenko
2021-01-28  7:01         ` Viresh Kumar
2021-02-01  0:21     ` Chanwoo Choi
2021-02-01 19:57     ` 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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