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

Stefan Agner
2016-10-10T21:06:53Z

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. The set_polarity callback should get called in case a
different polarity is requested.

> 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.

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.

--
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;