linux-kernel - Re: [PATCH] opp: Provide a function for just setting bandwidth

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Message-ID: <cbea8bc5-5dd2-b097-964d-3494935d4f68@linaro.org>
Date:   Mon, 29 May 2023 11:35:06 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] opp: Provide a function for just setting bandwidth



On 29.05.2023 06:58, Viresh Kumar wrote:
> On 26-05-23, 12:59, Konrad Dybcio wrote:
>> There are some users which have tight power sequencing requirements,
>> like the Qualcomm Adreno GPU.
>>
>> Dropping the entire OPP kills clocks, bw and required-opps at once,
>> but on certain Adrenos we need something like:
>>
>>
>> disable memory clock (clk)
>> disable all other clocks, including the opp-managed core clock (clk_bulk)
>> kill one, fully manually controlled genpd (manual runtime pm)
>> remove bus vote (func proposed in this patch)
>> kill another genpd (manual runtime pm)
>> kill the opp-managed genpd (automatic pm calls)
>>
>> Changing the order kills the chip until you reboot the whole board and
>> setting freq=0 using dev_pm_opp_set_rate doesn't drop the bw vote.
> 
> I am a bit confused now.
> 
> What's the exact problem with dev_pm_opp_set_rate(dev, 0) ? It does set the
> bandwidth too, from what I can see.
I think I didn't state my intentions correctly..

The proposed function would set *just* the bandwidth through OPP,
so it'd be essentially equal to

loop over num_paths {
	icc_get(...)

	icc_set(...)

	icc_put(...)
}

but since OPP already picked up these interconnect paths, it makes
little sense to mess with them through raw APIs.

Konrad
>