linux-kernel - Re: [PATCH 0/3] opp: Add bw_factor support to adjust bandwidth dynamically

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Message-ID: <20250811084453.ocibslv6kxkib6po@vireshk-i7>
Date: Mon, 11 Aug 2025 14:14:53 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Cc: Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
	Stephen Boyd <sboyd@...nel.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Manivannan Sadhasivam <mani@...nel.org>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kwilczynski@...nel.org>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 0/3] opp: Add bw_factor support to adjust bandwidth
 dynamically

Sorry for the delay, I was travelling a bit recently.

On 06-08-25, 10:35, Krishna Chaitanya Chundru wrote:
> On 8/4/2025 4:43 PM, Viresh Kumar wrote:
> > On 01-08-25, 15:05, Krishna Chaitanya Chundru wrote:
> > > Currently we are fetching the OPP based on the frequency and setting
> > > that OPP using dev_pm_opp_set_opp().
> > > 
> > > As you are suggesting to use dev_pm_opp_set_prop_name() here.
> > > This what I understood
> > > 
> > > First set prop name using dev_pm_opp_set_prop_name then
> > > set opp dev_pm_opp_set_opp()
> > > 
> > > if you want to change above one we need to first clear using
> > > dev_pm_opp_put_prop_name() then again call dev_pm_opp_set_prop_name
> > > & dev_pm_opp_set_opp()
> > 
> > dev_pm_opp_set_prop_name() should be called only once at boot time and not
> > again later on. It is there to configure one of the named properties before the
> > OPP table initializes for a device. Basically it is there to select one of the
> > available properties for an OPP, like selecting a voltage applicable for an OPP
> > for a device.
>
> Then we can't use this dev_pm_opp_set_prop_name(), there is possibility
> link width x1, x2, x4 etc can also change at runtime.

Hmm, looking at the way you have implemented the bw multiplier, you
are going to call that every time you need to change the OPP
configuration. That doesn't look nice TBH. Such configurations are
normally provided via DT or are configured once at boot and not
touched after that. What you are basically doing is something like,
adding a single OPP in DT and changing the OPP frequency right before
setting it at runtime.

FWIW, you are allowed to add multiple OPPs with same frequency value
but different bandwidths or levels. I think you should use that and
correctly describe the hardware first (which is the step in the right
direction). And then you can find the right OPP at runtime and send a
request to configure it. That way we can avoid adding hacks in the OPP
core.

-- 
viresh