Re: [PATCH v3 3/6] pwm: imx: support output polarity inversion

Lukasz Majewski
2016-10-13T05:54:46Z

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Hi Stefan,

> On 2016-10-12 15:15, Lukasz Majewski wrote:
> > Hi Stefan,
> >
> >> On 2016-10-07 08:11, Bhuvanchandra DV wrote:
> >> > From: Lothar Wassmann <LW@KARO-electronics.de>
> >> >
> >> > The i.MX pwm unit on i.MX27 and newer SoCs provides a
> >> > configurable output polarity. This patch adds support to utilize
> >> > this feature where available.
> >> >
> >> > Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
> >> > Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
> >> > Signed-off-by: Bhuvanchandra DV <bhuvanchandra.dv@toradex.com>
> >> > Acked-by: Shawn Guo <shawn.guo@linaro.org>
> >> > Reviewed-by: Sascha Hauer <s.hauer@pengutronix.de>
> >> > ---
> >> > Documentation/devicetree/bindings/pwm/imx-pwm.txt | 6 +--
> >> > drivers/pwm/pwm-imx.c | 51
> >> > +++++++++++++++++++++-- 2 files changed, 51 insertions(+), 6
> >> > deletions(-)
> >> >
> >> > diff --git a/Documentation/devicetree/bindings/pwm/imx-pwm.txt
> >> > b/Documentation/devicetree/bindings/pwm/imx-pwm.txt
> >> > index e00c2e9..c61bdf8 100644
> >> > --- a/Documentation/devicetree/bindings/pwm/imx-pwm.txt
> >> > +++ b/Documentation/devicetree/bindings/pwm/imx-pwm.txt
> >> > @@ -6,8 +6,8 @@ Required properties:
> >> > - "fsl,imx1-pwm" for PWM compatible with the one integrated on
> >> > i.MX1
> >> > - "fsl,imx27-pwm" for PWM compatible with the one integrated
> >> > on i.MX27
> >> > - reg: physical base address and length of the controller's
> >> > registers -- #pwm-cells: should be 2. See pwm.txt in this
> >> > directory for a description of
> >> > - the cells format.
> >> > +- #pwm-cells: 2 for i.MX1 and 3 for i.MX27 and newer SoCs. See
> >> > pwm.txt
> >> > + in this directory for a description of the cells format.
> >> > - clocks : Clock specifiers for both ipg and per clocks.
> >> > - clock-names : Clock names should include both "ipg" and "per"
> >> > See the clock consumer binding,
> >> > @@ -17,7 +17,7 @@ See the clock consumer binding,
> >> > Example:
> >> >
> >> > pwm1: pwm@53fb4000 {
> >> > - #pwm-cells = <2>;
> >> > + #pwm-cells = <3>;
> >> > compatible = "fsl,imx53-pwm", "fsl,imx27-pwm";
> >> > reg = <0x53fb4000 0x4000>;
> >> > clocks = <&clks IMX5_CLK_PWM1_IPG_GATE>,
> >> > diff --git a/drivers/pwm/pwm-imx.c b/drivers/pwm/pwm-imx.c
> >> > index d600fd5..c37d223 100644
> >> > --- a/drivers/pwm/pwm-imx.c
> >> > +++ b/drivers/pwm/pwm-imx.c
> >> > @@ -38,6 +38,7 @@
> >> > #define MX3_PWMCR_DOZEEN (1 << 24)
> >> > #define MX3_PWMCR_WAITEN (1 << 23)
> >> > #define MX3_PWMCR_DBGEN (1 << 22)
> >> > +#define MX3_PWMCR_POUTC (1 << 18)
> >> > #define MX3_PWMCR_CLKSRC_IPG_HIGH (2 << 16)
> >> > #define MX3_PWMCR_CLKSRC_IPG (1 << 16)
> >> > #define MX3_PWMCR_SWR (1 << 3)
> >> > @@ -180,6 +181,9 @@ static int imx_pwm_config_v2(struct pwm_chip
> >> > *chip, if (enable)
> >> > cr |= MX3_PWMCR_EN;
> >> >
> >> > + if (pwm->args.polarity == PWM_POLARITY_INVERSED)
> >> > + cr |= MX3_PWMCR_POUTC;
> >> > +
> >>
> >> This seems wrong to me, the config callback is meant for
> >> period/duty cycle only.
> >
> > If it is meant only for that, then the polarity should be removed
> > from it.
> >
> > However after very quick testing, at least on my setup, it turns out
> > that removing this lines causes polarity to _not_ being set (and the
> > polarity is not inverted).
> >
> > I will investigate this further on my setup and hopefully sent
> > proper patch.
> >
> >> The set_polarity callback should get called in case a
> >> different polarity is requested.
> >
> > On my setup the pwm2 is set from DT and pwm_backlight_probe() calls
> > pwm_apply_args(), so everything should work. However, as I mentioned
> > above there still is some problem with inversion setting.
> >
> >>
> >>
> >> > writel(cr, imx->mmio_base + MX3_PWMCR);
> >> >
> >> > return 0;
> >> > @@ -240,27 +244,62 @@ static void imx_pwm_disable(struct pwm_chip
> >> > *chip, struct pwm_device *pwm)
> >> > clk_disable_unprepare(imx->clk_per);
> >> > }
> >> >
> >> > -static struct pwm_ops imx_pwm_ops = {
> >> > +static int imx_pwm_set_polarity(struct pwm_chip *chip, struct
> >> > pwm_device *pwm,
> >> > + enum pwm_polarity polarity)
> >> > +{
> >> > + struct imx_chip *imx = to_imx_chip(chip);
> >> > + u32 val;
> >> > +
> >> > + if (polarity == pwm->args.polarity)
> >> > + return 0;
> >>
> >> I don't think that this is right. Today, pwm_apply_args (in
> >> include/linux/pwm.h) copies the polarity from args to
> >> state.polarity, which is then passed as polarity argument to this
> >> function. So this will always return 0 afaict.
> >
> > Yes, I've overlooked it (that the state is copied).
> >
> > It can be dropped.
>
> Did you do the above test with that line dropped?

Yes. The above code has been also removed.

Best regards,
Łukasz Majewski

>
> >
> >>
> >> I would just drop that.
> >>
> >> There is probably one little problem in the current state of
> >> affairs: If the bootloader makes use of a PWM channel with
> >> inverted state, then the kernel would not know about that and
> >> currently assume a wrong initial state... I guess at one point in
> >> time we should implement the state retrieval callback and move to
> >> the new atomic PWM API, which would mean to implement apply
> >> callback.
> >
> > Are there any patches on the horizon?
> >
>
> Not that I know of...
>
> --
> Stefan
>
> >>
> >> --
> >> Stefan
> >>
> >>
> >> > +
> >> > + val = readl(imx->mmio_base + MX3_PWMCR);
> >> > +
> >> > + if (polarity == PWM_POLARITY_INVERSED)
> >> > + val |= MX3_PWMCR_POUTC;
> >> > + else
> >> > + val &= ~MX3_PWMCR_POUTC;
> >> > +
> >> > + writel(val, imx->mmio_base + MX3_PWMCR);
> >> > +
> >> > + dev_dbg(imx->chip.dev, "%s: polarity set to %s\n",
> >> > __func__,
> >> > + polarity == PWM_POLARITY_INVERSED ? "inverted" :
> >> > "normal"); +
> >> > + return 0;
> >> > +}
> >> > +
> >> > +static struct pwm_ops imx_pwm_ops_v1 = {
> >> > .enable = imx_pwm_enable,
> >> > .disable = imx_pwm_disable,
> >> > .config = imx_pwm_config,
> >> > .owner = THIS_MODULE,
> >> > };
> >> >
> >> > +static struct pwm_ops imx_pwm_ops_v2 = {
> >> > + .enable = imx_pwm_enable,
> >> > + .disable = imx_pwm_disable,
> >> > + .set_polarity = imx_pwm_set_polarity,
> >> > + .config = imx_pwm_config,
> >> > + .owner = THIS_MODULE,
> >> > +};
> >> > +
> >> > struct imx_pwm_data {
> >> > int (*config)(struct pwm_chip *chip,
> >> > struct pwm_device *pwm, int duty_ns, int
> >> > period_ns); void (*set_enable)(struct pwm_chip *chip, bool
> >> > enable);
> >> > + struct pwm_ops *pwm_ops;
> >> > };
> >> >
> >> > static struct imx_pwm_data imx_pwm_data_v1 = {
> >> > .config = imx_pwm_config_v1,
> >> > .set_enable = imx_pwm_set_enable_v1,
> >> > + .pwm_ops = &imx_pwm_ops_v1,
> >> > };
> >> >
> >> > static struct imx_pwm_data imx_pwm_data_v2 = {
> >> > .config = imx_pwm_config_v2,
> >> > .set_enable = imx_pwm_set_enable_v2,
> >> > + .pwm_ops = &imx_pwm_ops_v2,
> >> > };
> >> >
> >> > static const struct of_device_id imx_pwm_dt_ids[] = {
> >> > @@ -282,6 +321,8 @@ static int imx_pwm_probe(struct
> >> > platform_device *pdev) if (!of_id)
> >> > return -ENODEV;
> >> >
> >> > + data = of_id->data;
> >> > +
> >> > imx = devm_kzalloc(&pdev->dev, sizeof(*imx),
> >> > GFP_KERNEL); if (imx == NULL)
> >> > return -ENOMEM;
> >> > @@ -300,18 +341,22 @@ static int imx_pwm_probe(struct
> >> > platform_device *pdev) return PTR_ERR(imx->clk_ipg);
> >> > }
> >> >
> >> > - imx->chip.ops = &imx_pwm_ops;
> >> > + imx->chip.ops = data->pwm_ops;
> >> > imx->chip.dev = &pdev->dev;
> >> > imx->chip.base = -1;
> >> > imx->chip.npwm = 1;
> >> > imx->chip.can_sleep = true;
> >> > + if (data->pwm_ops->set_polarity) {
> >> > + dev_dbg(&pdev->dev, "PWM supports output
> >> > inversion\n");
> >> > + imx->chip.of_xlate = of_pwm_xlate_with_flags;
> >> > + imx->chip.of_pwm_n_cells = 3;
> >> > + }
> >> >
> >> > r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> >> > imx->mmio_base = devm_ioremap_resource(&pdev->dev, r);
> >> > if (IS_ERR(imx->mmio_base))
> >> > return PTR_ERR(imx->mmio_base);
> >> >
> >> > - data = of_id->data;
> >> > imx->config = data->config;
> >> > imx->set_enable = data->set_enable;
> >>
> >
> > Best regards,
> >
> > Łukasz Majewski

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