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

Lukasz Majewski
2016-10-20T09:46:40Z

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Hi Stefan,

> 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.

Unfortunately, it also resets the PWM IP block and setups it again (by
writing to PWMCR register). In that function we setup for example MX3_PWMCR_DOZEEN
and MX3_PWMCR_DBGEN. Why cannot we setup polarity as well?

I've double checked the backlight and pwm code flow.

Please find following snippet:

[ 0.135545] ######### imx_pwm_probe
[ 0.135581] PWM supports output inversion
[ 0.136864] ######### pwm_backlight_probe
[ 0.136913] backlight supply power not found, using dummy regulator
[ 0.136984] ######### imx_pwm_set_polarity 1
[ 0.136995] imx_pwm_set_polarity: polarity set to inverted cr: 0x40000 0xf08f8000
[ 0.137005] #########0 imx_pwm_config_v2 cr: 0x40000
[ 0.137683] #########1 imx_pwm_config_v2 cr: 0x0 0xf08f8000
[ 0.137693] #########2 imx_pwm_config_v2 cr: 0x1c20050
[ 0.137702] #########3 imx_pwm_config_v2 cr: 0x1c20050 0xf08f8000
[ 0.137711] @@@@@@@@@@ pwm_apply_state

Here the pwm_backlight_probe calls set_polarity callback available in
pwm - the polarity is set (the 0x40000 value).

The above operation is performed in pwm_apply_state (@ drivers/pwm/core.c).
In the same function, latter we call the pwm->chip->ops->config(), which is the
pointer to config_v2.
Since the PWM is not yet enabled, this function performs SW reset and
PWM inversion setting is cleared.

Possible solutions:

1. Leave the original patch from Bhuvanchandra as it was (I'm for this
option)

2. Enable early PWM (in core, or in bl driver) so the config_v2 is not
calling SW reset on the PWM. (but this solutions seems _really_ bad to me)

3. Perform defer probe of pwm backlight driver (pwm_bl.c) until the pwm
is fully configured (it might be a bit tricky).

Best regards,
Łukasz Majewski

> > >
> > > 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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