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Date: Mon, 12 Apr 2021 11:55:36 +0900
From: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@...hiba.co.jp>
To: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc: Rob Herring <robh+dt@...nel.org>,
Thierry Reding <thierry.reding@...il.com>,
Lee Jones <lee.jones@...aro.org>, devicetree@...r.kernel.org,
linux-pwm@...r.kernel.org, punit1.agrawal@...hiba.co.jp,
yuji2.ishikawa@...hiba.co.jp, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] pwm: visconti: Add Toshiba Visconti SoC PWM
support
Hi Uwe,
Thanks for your review.
On Sat, Apr 10, 2021 at 03:53:21PM +0200, Uwe Kleine-König wrote:
> Hello,
>
> just a few small details left to criticize ...
>
> On Sat, Apr 10, 2021 at 08:08:37AM +0900, Nobuhiro Iwamatsu wrote:
> > diff --git a/drivers/pwm/pwm-visconti.c b/drivers/pwm/pwm-visconti.c
> > new file mode 100644
> > index 000000000000..99d83f94ed86
> > --- /dev/null
> > +++ b/drivers/pwm/pwm-visconti.c
> > @@ -0,0 +1,188 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * Toshiba Visconti pulse-width-modulation controller driver
> > + *
> > + * Copyright (c) 2020 TOSHIBA CORPORATION
> > + * Copyright (c) 2020 Toshiba Electronic Devices & Storage Corporation
> > + *
> > + * Authors: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@...hiba.co.jp>
> > + *
> > + */
> > +
> > +#include <linux/err.h>
> > +#include <linux/io.h>
> > +#include <linux/module.h>
> > +#include <linux/of_device.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/pwm.h>
> > +
> > +#define PIPGM_PCSR(ch) (0x400 + 4 * (ch))
> > +#define PIPGM_PDUT(ch) (0x420 + 4 * (ch))
> > +#define PIPGM_PWMC(ch) (0x440 + 4 * (ch))
> > +
> > +#define PIPGM_PWMC_PWMACT BIT(5)
> > +#define PIPGM_PWMC_CLK_MASK GENMASK(1, 0)
> > +#define PIPGM_PWMC_POLARITY_MASK GENMASK(5, 5)
> > +
> > +struct visconti_pwm_chip {
> > + struct pwm_chip chip;
> > + void __iomem *base;
> > +};
> > +
> > +static inline struct visconti_pwm_chip *to_visconti_chip(struct pwm_chip *chip)
> > +{
> > + return container_of(chip, struct visconti_pwm_chip, chip);
> > +}
> > +
> > +static int visconti_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> > + const struct pwm_state *state)
> > +{
> > + struct visconti_pwm_chip *priv = to_visconti_chip(chip);
> > + u32 period, duty_cycle, pwmc0;
> > +
> > + /*
> > + * pwmc is a 2-bit divider for the input clock running at 1 MHz.
> > + * When the settings of the PWM are modified, the new values are shadowed in hardware until
> > + * the period register (PCSR) is written and the currently running period is completed. This
> > + * way the hardware switches atomically from the old setting to the new.
> > + * Also, disabling the hardware completes the currently running period and keeps the output
> > + * at low level at all times.
>
> Can you please put a paragraph analogous to the one in pwm-sifive in the
> same format. This simplified keeping an overview about the oddities of
> the various supported chips.
OK, I will check pwm-sifive's, and add.
>
> > + */
> > + if (!state->enabled) {
> > + writel(0, priv->base + PIPGM_PCSR(pwm->hwpwm));
> > + return 0;
> > + }
> > +
> > [...]
> > +
> > +static void visconti_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> > + struct pwm_state *state)
> > +{
> > + struct visconti_pwm_chip *priv = chip_to_priv(chip);
> > + u32 period, duty, pwmc0, pwmc0_clk;
> > +
> > + period = readl(priv->base + PIPGM_PCSR(pwm->hwpwm));
> > + if (period)
> > + state->enabled = true;
> > + else
> > + state->enabled = false;
>
> If PIPGM_PCSR is 0 the hardware is still active and setting a new
> configuration completes the currently running period, right? Then I
> think having always state->enabled = true is a better match.
>
If PIPGM_PCSR is 0, the hardware is stopped. Even if the settings of
other registers are written, the values of other registers will not work
unless PIPGM_PCSR is written.
However, as a logic, if PIPGM_PCSR becomes 0, it is only
visconti_pwm_apply () in this driver,
so I think that this process should always be state-> enabled = true
as you pointed out.
I wil drop this, thanks.
> > + duty = readl(priv->base + PIPGM_PDUT(pwm->hwpwm));
> > + pwmc0 = readl(priv->base + PIPGM_PWMC(pwm->hwpwm));
> > + pwmc0_clk = pwmc0 & PIPGM_PWMC_CLK_MASK;
> > +
> > + state->period = (period << pwmc0_clk) * NSEC_PER_USEC;
> > + state->duty_cycle = (duty << pwmc0_clk) * NSEC_PER_USEC;
> > + if (pwmc0 & PIPGM_PWMC_POLARITY_MASK)
> > + state->polarity = PWM_POLARITY_INVERSED;
> > + else
> > + state->polarity = PWM_POLARITY_NORMAL;
> > +}
> > +
> > [...]
> > +
> > +static int visconti_pwm_probe(struct platform_device *pdev)
> > +{
> > + struct device *dev = &pdev->dev;
> > + struct visconti_pwm_chip *priv;
> > + int ret;
> > +
> > + priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> > + if (!priv)
> > + return -ENOMEM;
> > +
> > + priv->base = devm_platform_ioremap_resource(pdev, 0);
> > + if (IS_ERR(priv->base))
> > + return PTR_ERR(priv->base);
> > +
> > + platform_set_drvdata(pdev, priv);
> > +
> > + priv->chip.dev = dev;
> > + priv->chip.ops = &visconti_pwm_ops;
> > + priv->chip.npwm = 4;
> > +
> > + ret = pwmchip_add(&priv->chip);
> > + if (ret < 0)
> > + return dev_err_probe(&pdev->dev, ret, "Cannot register visconti PWM\n");
>
> Thierry told to have picked up my patch to add the function
> devm_pwmchip_add. I just double checked and it didn't made it into his
> for-next branch yet. When you respin this series please check if the
> patch landed in the mean time and then make use of it.
>
OKay.
> > + return 0;
> > +}
>
> Best regards
> Uwe
Best regards,
Nobuhiro
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