linux-kernel - Re: [PATCH V2 24/30] serial: qcom: Migrate to dev_pm_opp_set

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Date:   Fri, 1 Jul 2022 14:54:58 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Jiri Slaby <jirislaby@...nel.org>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>, Nishanth Menon <nm@...com>,
        linux-arm-msm@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 24/30] serial: qcom: Migrate to dev_pm_opp_set_config()

On 01-07-22, 10:44, Greg Kroah-Hartman wrote:
> On Fri, Jul 01, 2022 at 01:50:19PM +0530, Viresh Kumar wrote:
> > diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
> > +	struct dev_pm_opp_config config = {
> > +		.clk_names = (const char *[]){ "se" },
> > +		.clk_count = 1,
> > +	};
> >  
> > -	ret = devm_pm_opp_set_clkname(&pdev->dev, "se");
> > +	ret = devm_pm_opp_set_config(&pdev->dev, &config);
> 
> This feels like a step back.  This is much harder now, what's wrong with
> devm_pm_opp_set_clkname() as is?

Hi Greg,

There are a number of configurations one can do for a device's OPP
table currently:

- clk, single or multiple (new)
- helper to configure multiple clocks (for multiple clocks)
- supplies or regulators
- helper to configure supplies (for multiple supplies)
- OPP supported-hw property
- OPP Property-name
- Genpd specific one
- etc

One problem was that it was a mess within the OPP core with a separate
interface for each of these interfaces, almost duplicate code, etc.

But then it was a bigger mess for the user drivers that need to manage
a few of these. They were required to call multiple APIs, with all the
interfaces returning tokens, which the callers need to save and supply
back to free the resources later. More code, hard to manage, easy to
abuse and add bugs to.

The new interface makes it easier and clean for everyone and allows
easy upgrades of interfaces in future. Adding a new interface, like
support for multiple clocks for a device that I just did, is much
easier now.

I really believe this is a step in the right direction :)

-- 
viresh