linux-kernel - RE: [v3 2/3] pwm: Add Aspeed ast2600 PWM support

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Message-ID: <OS0PR01MB592234A33E67C1318F58135A863C9@OS0PR01MB5922.jpnprd01.prod.outlook.com>
Date:   Mon, 7 Nov 2022 09:38:44 +0000
From:   Biju Das <biju.das.jz@...renesas.com>
To:     Billy Tsai <billy_tsai@...eedtech.com>,
        "jdelvare@...e.com" <jdelvare@...e.com>,
        "linux@...ck-us.net" <linux@...ck-us.net>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "joel@....id.au" <joel@....id.au>,
        "andrew@...id.au" <andrew@...id.au>,
        "lee.jones@...aro.org" <lee.jones@...aro.org>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "u.kleine-koenig@...gutronix.de" <u.kleine-koenig@...gutronix.de>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
        BMC-SW <BMC-SW@...eedtech.com>,
        "garnermic@...a.com" <garnermic@...a.com>
CC:     kernel test robot <lkp@...el.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: RE: [v3 2/3] pwm: Add Aspeed ast2600 PWM support

> Subject: RE: [v3 2/3] pwm: Add Aspeed ast2600 PWM support
> 
> Hi Billy Tsai,
> 
> > -----Original Message-----
> > From: Billy Tsai <billy_tsai@...eedtech.com>
> > Sent: 07 November 2022 09:26
> > To: Biju Das <biju.das.jz@...renesas.com>; jdelvare@...e.com;
> > linux@...ck- us.net; robh+dt@...nel.org; joel@....id.au;
> > andrew@...id.au; lee.jones@...aro.org; thierry.reding@...il.com;
> > u.kleine- koenig@...gutronix.de; p.zabel@...gutronix.de;
> > linux-hwmon@...r.kernel.org; devicetree@...r.kernel.org;
> > linux-arm-kernel@...ts.infradead.org; linux- aspeed@...ts.ozlabs.org;
> > linux-kernel@...r.kernel.org; linux- pwm@...r.kernel.org; BMC-SW
> > <BMC-SW@...eedtech.com>; garnermic@...a.com
> > Cc: kernel test robot <lkp@...el.com>; Geert Uytterhoeven
> > <geert+renesas@...der.be>
> > Subject: Re: [v3 2/3] pwm: Add Aspeed ast2600 PWM support
> >
> > On 2022/11/7, 4:55 PM, "Biju Das" <biju.das.jz@...renesas.com> wrote:
> >
> >     > > -----Original Message-----
> >     > > From: Billy Tsai <billy_tsai@...eedtech.com>
> >     > > Sent: 07 November 2022 08:48
> >     > > To: Biju Das <biju.das.jz@...renesas.com>; jdelvare@...e.com;
> > linux@...ck-
> >     > > us.net; robh+dt@...nel.org; joel@....id.au; andrew@...id.au;
> >     > > lee.jones@...aro.org; thierry.reding@...il.com; u.kleine-
> >     > > koenig@...gutronix.de; p.zabel@...gutronix.de; linux-
> > hwmon@...r.kernel.org;
> >     > > devicetree@...r.kernel.org;
> > linux-arm-kernel@...ts.infradead.org;
> > linux-
> >     > > aspeed@...ts.ozlabs.org; linux-kernel@...r.kernel.org; linux-
> >     > > pwm@...r.kernel.org; BMC-SW <BMC-SW@...eedtech.com>;
> > garnermic@...a.com
> >     > > Cc: kernel test robot <lkp@...el.com>
> >     > > Subject: Re: [v3 2/3] pwm: Add Aspeed ast2600 PWM support
> >     > >
> >     > > On 2022/11/2, 11:56 PM, "Biju Das"
> > <biju.das.jz@...renesas.com>
> > wrote:
> >     > >
> >     > >     > > +	parent_dev = of_find_device_by_node(np);
> >     > >     > > +	priv->clk = devm_clk_get_enabled(&parent_dev->dev,
> NULL);
> >     > >     > > +	if (IS_ERR(priv->clk))
> >     > >     > > +		return dev_err_probe(dev, PTR_ERR(priv->clk),
> >     > >     > > +				     "Couldn't get clock\n");
> >     > >
> >     > >     > What is the use case?
> >     > >
> >     > >     > Is pwm configured by boot loader initially ?
> >     > >
> >     > >     > Or
> >     > >
> >     > >     > pwm configured by Linux, not by the bootloader initially?
> >     > >
> >     > >     > Or
> >     > >
> >     > >     > Driver needs to handle both cases?
> >     > >
> >     > >     > Just asking, because you are turning on the clock
> unnecessarily
> > here,
> >     > >     > If you need to address all the use cases. If it is just first
> > one, then
> >     > >     > It is ok.
> >     > >
> >     > > Hi Biju,
> >     > >
> >     > > The driver want to handle all of the use cases. Can you tell
> > me why turning
> >     > > on the clock is unnecessarily here?
> >
> >     > For the use case, "pwm configured by Linux, not by the
> > bootloader initially",
> >
> >     > You are unnecessarily turning on the clocks. You could
> >
> >     > enable it during pwm_enable
> >     > and disable it during pwm_disable.
> >
> >     > For configuring registers, while pwm is in disable state,
> >     > you could just turn on the clock and do the register
> > configurations and turn it off.
> >
> >     > By this way you are saving power.
> >
> > Hi Biju,
> >
> > This clock is the source clock for the pwm controller (include the
> > accessing for the register).
> 
> OK, But the driver has only one clock (priv->clk =
> devm_clk_get_enabled(&parent_dev->dev, NULL)).
> You are always turning it on during probe.

Your system needs this clock always on, then it is OK.

Cheers,
Biju