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SubjectRE: [v3 2/3] pwm: Add Aspeed ast2600 PWM support
Date
> Subject: RE: [v3 2/3] pwm: Add Aspeed ast2600 PWM support
>
> Hi Billy Tsai,
>
> > -----Original Message-----
> > From: Billy Tsai <billy_tsai@aspeedtech.com>
> > Sent: 07 November 2022 09:26
> > To: Biju Das <biju.das.jz@bp.renesas.com>; jdelvare@suse.com;
> > linux@roeck- us.net; robh+dt@kernel.org; joel@jms.id.au;
> > andrew@aj.id.au; lee.jones@linaro.org; thierry.reding@gmail.com;
> > u.kleine- koenig@pengutronix.de; p.zabel@pengutronix.de;
> > linux-hwmon@vger.kernel.org; devicetree@vger.kernel.org;
> > linux-arm-kernel@lists.infradead.org; linux- aspeed@lists.ozlabs.org;
> > linux-kernel@vger.kernel.org; linux- pwm@vger.kernel.org; BMC-SW
> > <BMC-SW@aspeedtech.com>; garnermic@meta.com
> > Cc: kernel test robot <lkp@intel.com>; Geert Uytterhoeven
> > <geert+renesas@glider.be>
> > Subject: Re: [v3 2/3] pwm: Add Aspeed ast2600 PWM support
> >
> > On 2022/11/7, 4:55 PM, "Biju Das" <biju.das.jz@bp.renesas.com> wrote:
> >
> > > > -----Original Message-----
> > > > From: Billy Tsai <billy_tsai@aspeedtech.com>
> > > > Sent: 07 November 2022 08:48
> > > > To: Biju Das <biju.das.jz@bp.renesas.com>; jdelvare@suse.com;
> > linux@roeck-
> > > > us.net; robh+dt@kernel.org; joel@jms.id.au; andrew@aj.id.au;
> > > > lee.jones@linaro.org; thierry.reding@gmail.com; u.kleine-
> > > > koenig@pengutronix.de; p.zabel@pengutronix.de; linux-
> > hwmon@vger.kernel.org;
> > > > devicetree@vger.kernel.org;
> > linux-arm-kernel@lists.infradead.org;
> > linux-
> > > > aspeed@lists.ozlabs.org; linux-kernel@vger.kernel.org; linux-
> > > > pwm@vger.kernel.org; BMC-SW <BMC-SW@aspeedtech.com>;
> > garnermic@meta.com
> > > > Cc: kernel test robot <lkp@intel.com>
> > > > Subject: Re: [v3 2/3] pwm: Add Aspeed ast2600 PWM support
> > > >
> > > > On 2022/11/2, 11:56 PM, "Biju Das"
> > <biju.das.jz@bp.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


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