Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <f8731d93-b335-6d9a-183c-34a652f45455@linaro.org>
Date:   Fri, 26 May 2023 12:59:17 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.11.0
Content-Language: en-US
To:     Viresh Kumar <viresh.kumar@linaro.org>
Cc:     Viresh Kumar <vireshk@kernel.org>, Nishanth Menon <nm@ti.com>,
        Stephen Boyd <sboyd@kernel.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Marijn Suijten <marijn.suijten@somainline.org>,
        linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20230526-topic-opp_bw-v1-1-e881091363af@linaro.org>
 <20230526105320.pfnu3oxl2cm37ot7@vireshk-i7>
From:   Konrad Dybcio <konrad.dybcio@linaro.org>
Subject: Re: [PATCH] opp: Provide a function for just setting bandwidth
In-Reply-To: <20230526105320.pfnu3oxl2cm37ot7@vireshk-i7>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 26.05.2023 12:53, Viresh Kumar wrote:
> On 26-05-23, 11:17, Konrad Dybcio wrote:
>> Currently it's not possible to set just the bandwidth if the OPP
>> describes other properties (required-opps, opp-hz etc.).
>>
>> Introduce dev_pm_opp_set_bw() to solve this problem.
> 
> The OPP core (intentionally) doesn't provide any such interface for
> freq, volt, bw, level, etc.
> 
> Setting just one of the properties for a device is potentially harmful and the
> OPP must be set as a whole and so this isn't allowed. There is
> dev_pm_opp_set_freq(), but it uses freq to just find the OPP and sets entire OPP
> only.
> 
> Why should be break this for bw ?
> 
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.

Konrad