Hi Billy Tsai, > -----Original Message----- > From: Billy Tsai <billy_tsai@xxxxxxxxxxxxxx> > Sent: 07 November 2022 09:26 > To: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>; jdelvare@xxxxxxxx; linux@roeck- > us.net; robh+dt@xxxxxxxxxx; joel@xxxxxxxxx; andrew@xxxxxxxx; > lee.jones@xxxxxxxxxx; thierry.reding@xxxxxxxxx; u.kleine- > koenig@xxxxxxxxxxxxxx; p.zabel@xxxxxxxxxxxxxx; linux-hwmon@xxxxxxxxxxxxxxx; > devicetree@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux- > aspeed@xxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux- > pwm@xxxxxxxxxxxxxxx; BMC-SW <BMC-SW@xxxxxxxxxxxxxx>; garnermic@xxxxxxxx > Cc: kernel test robot <lkp@xxxxxxxxx>; Geert Uytterhoeven > <geert+renesas@xxxxxxxxx> > Subject: Re: [v3 2/3] pwm: Add Aspeed ast2600 PWM support > > On 2022/11/7, 4:55 PM, "Biju Das" <biju.das.jz@xxxxxxxxxxxxxx> wrote: > > > > -----Original Message----- > > > From: Billy Tsai <billy_tsai@xxxxxxxxxxxxxx> > > > Sent: 07 November 2022 08:48 > > > To: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>; jdelvare@xxxxxxxx; > linux@roeck- > > > us.net; robh+dt@xxxxxxxxxx; joel@xxxxxxxxx; andrew@xxxxxxxx; > > > lee.jones@xxxxxxxxxx; thierry.reding@xxxxxxxxx; u.kleine- > > > koenig@xxxxxxxxxxxxxx; p.zabel@xxxxxxxxxxxxxx; linux- > hwmon@xxxxxxxxxxxxxxx; > > > devicetree@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; > linux- > > > aspeed@xxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux- > > > pwm@xxxxxxxxxxxxxxx; BMC-SW <BMC-SW@xxxxxxxxxxxxxx>; > garnermic@xxxxxxxx > > > Cc: kernel test robot <lkp@xxxxxxxxx> > > > Subject: Re: [v3 2/3] pwm: Add Aspeed ast2600 PWM support > > > > > > On 2022/11/2, 11:56 PM, "Biju Das" <biju.das.jz@xxxxxxxxxxxxxx> > 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. > For the output of the PWM (pwm_enable/pwm_disable), the controller have > another register to control it. That is enable/disable register for controlling the output of PWM. Cheers, Biju
