From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jon Hunter Subject: Re: [PATCH V3] pwm: tegra: dynamic clk freq configuration by PWM driver Date: Tue, 26 May 2020 13:05:53 +0100 Message-ID: <81646862-8cbd-95f1-506d-ea375e365d69@nvidia.com> References: <1590492335-25857-1-git-send-email-spatra@nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <1590492335-25857-1-git-send-email-spatra@nvidia.com> Content-Language: en-US Sender: linux-pwm-owner@vger.kernel.org To: Sandipan Patra , treding@nvidia.com, u.kleine-koenig@pengutronix.de Cc: bbasu@nvidia.com, ldewangan@nvidia.com, kyarlagadda@nvidia.com, linux-pwm@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-tegra@vger.kernel.org On 26/05/2020 12:25, Sandipan Patra wrote: > Added support for dynamic clock freq configuration in pwm kernel driver. > Earlier the pwm driver used to cache boot time clock rate by pwm clock > parent during probe. Hence dynamically changing pwm frequency was not > possible for all the possible ranges. With this change, dynamic calculati= on > is enabled and it is able to set the requested period from sysfs knob > provided the value is supported by clock source. >=20 > Changes mainly have 2 parts: > - T186 and later chips [1] > - T210 and prior chips [2] >=20 > For [1] - Changes implemented to set pwm period dynamically and > also checks added to allow only if requested period(ns) is > below or equals to higher range. >=20 > For [2] - Only checks if the requested period(ns) is below or equals > to higher range defined by max clock limit. The limitation > in T210 or prior chips are due to the reason of having only > one pwm-controller supporting multiple channels. But later > chips have multiple pwm controller instances each having > single channel support. >=20 > Signed-off-by: Sandipan Patra > --- >=20 > PATCH V3: > 1. Return -EINVAL if requested period does not fall inside limit. > 2. Store the new clock rate for further references. > 3. Varible name change reverted. > 4. Comments corrected and new comments are added. >=20 > drivers/pwm/pwm-tegra.c | 85 +++++++++++++++++++++++++++++++++++++++++++= +++--- > 1 file changed, 80 insertions(+), 5 deletions(-) >=20 > diff --git a/drivers/pwm/pwm-tegra.c b/drivers/pwm/pwm-tegra.c > index d26ed8f..c6e5dcf 100644 > --- a/drivers/pwm/pwm-tegra.c > +++ b/drivers/pwm/pwm-tegra.c > @@ -4,8 +4,35 @@ > * > * Tegra pulse-width-modulation controller driver > * > - * Copyright (c) 2010, NVIDIA Corporation. > - * Based on arch/arm/plat-mxc/pwm.c by Sascha Hauer We should not remove the above line as this is giving credit to the above developer. > + * Copyright (c) 2010-2020, NVIDIA Corporation. > + * > + * Overview of Tegra Pulse Width Modulator Register: > + * 1. 13-bit: Frequency division (SCALE) > + * 2. 8-bit : Puls division (DUTY) > + * 3. 1-bit : Enable bit > + * > + * The PWM clock frequency is divided by 256 before subdividing it based > + * on the programmable frequency division value to generate the required > + * frequency for PWM output. The maximum output frequency that can be > + * achieved is (max rate of source clock) / 256. > + * e.g. if source clock rate is 408 MHz, maximum output frequency can be= : > + * 408 MHz/256 =3D 1.6 MHz. > + * This 1.6 MHz frequency can further be divided using SCALE value in PW= M. > + * > + * PWM pulse width: 8 bits are usable [23:16] for varying pulse width. > + * To achieve 100% duty cycle, program Bit [24] of this register to > + * 1=E2=80=99b1. In which case the other bits [23:16] are set to don't c= are. > + * > + * Limitations: > + * - When PWM is disabled, the output is driven to inactive. > + * - It does not allow the current PWM period to complete and > + * stops abruptly. > + * > + * - If the register is reconfigured while PWM is running, > + * it does not complete the currently running period. > + * > + * - If the user input duty is beyond acceptible limits, > + * -EINVAL is returned. > */ > =20 > #include > @@ -41,6 +68,7 @@ struct tegra_pwm_chip { > struct reset_control*rst; > =20 > unsigned long clk_rate; > + unsigned long min_period_ns; > =20 > void __iomem *regs; > =20 > @@ -68,7 +96,7 @@ static int tegra_pwm_config(struct pwm_chip *chip, stru= ct pwm_device *pwm, > { > struct tegra_pwm_chip *pc =3D to_tegra_pwm_chip(chip); > unsigned long long c =3D duty_ns, hz; > - unsigned long rate; > + unsigned long rate, required_clk_rate; > u32 val =3D 0; > int err; > =20 > @@ -83,9 +111,51 @@ static int tegra_pwm_config(struct pwm_chip *chip, st= ruct pwm_device *pwm, > val =3D (u32)c << PWM_DUTY_SHIFT; > =20 > /* > + * Period in nano second has to be <=3D highest allowed period > + * based on max clock rate of the pwm controller. > + * > + * higher limit =3D max clock limit >> PWM_DUTY_WIDTH > + * lower limit =3D min clock limit >> PWM_DUTY_WIDTH >> PWM_SCALE_WIDT= H Not sure why we mention the lower limit if we are not testing this condition. Does not appear to be relevant here. Or should we be checking this as well? > + */ > + if (period_ns < pc->min_period_ns) > + return -EINVAL; Something does not seem right here. If this is the highest allowed period, shouldn't this variable be called 'max_period_ns'? > + > + /* > * Compute the prescaler value for which (1 << PWM_DUTY_WIDTH) > * cycles at the PWM clock rate will take period_ns nanoseconds. > + * > + * num_channels: If single instance of PWM controller has multiple > + * channels (e.g. Tegra210 or older) then it is not applicable to s/applicable/possible > + * configure separate clock rates to each of the channels, in such > + * case the value stored during probe will be referred. > + * > + * If every PWM controller instance has one channel respectively, i.e. > + * nums_channels =3D=3D 1 then only the clock rate can be modified > + * dynamically (e.g. Tegra186 or Tegra194). > */ > + if (pc->soc->num_channels =3D=3D 1) { > + /* > + * Rate is multiplied with 2^PWM_DUTY_WIDTH so that it matches > + * with the highest applicable rate that the controller can s/applicable/possible > + * provide. Any further lower value can be derived by setting > + * PFM bits[0:12]. > + * > + * required_clk_rate is a reference rate for source clock and > + * it is derived based on user requested period. By setting the > + * source clock rate as required_clk_rate, PWM controller will > + * be able to configure the requested period. > + */ > + required_clk_rate =3D > + (NSEC_PER_SEC / period_ns) << PWM_DUTY_WIDTH; > + > + err =3D clk_set_rate(pc->clk, required_clk_rate); > + if (err < 0) > + return -EINVAL; > + > + /* Store the new rate for further references */ > + pc->clk_rate =3D clk_get_rate(pc->clk); > + } > + > rate =3D pc->clk_rate >> PWM_DUTY_WIDTH;=20 > =20 > /* Consider precision in PWM_SCALE_WIDTH rate calculation */ > @@ -94,7 +164,7 @@ static int tegra_pwm_config(struct pwm_chip *chip, str= uct pwm_device *pwm, > =20 > /* > * Since the actual PWM divider is the register's frequency divider > - * field minus 1, we need to decrement to get the correct value to > + * field plus 1, we need to decrement to get the correct value to Technically, this is a comment fix not related to the current change and so should be a separate patch. However, I will defer to Thierry on how he would prefer to handle this. Cheers Jon --=20 nvpublic