Date:   Thu, 21 Apr 2022 01:52:02 -0700
From:   Prashant Malani <pmalani@...omium.org>
To:     Fabio Baltieri <fabiobaltieri@...omium.org>
Cc:     Benson Leung <bleung@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Lee Jones <lee.jones@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        chrome-platform@...ts.linux.dev, linux-pwm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Tzung-Bi Shih <tzungbi@...nel.org>
Subject: Re: [PATCH v5 2/4] pwm: pwm-cros-ec: add channel type support

On Thu, Apr 21, 2022 at 1:34 AM Fabio Baltieri
<fabiobaltieri@...omium.org> wrote:
>
> On Wed, Apr 20, 2022 at 05:55:35PM +0000, Prashant Malani wrote:
> > On Apr 20 14:15, Fabio Baltieri wrote:
> > > Add support for EC_PWM_TYPE_DISPLAY_LIGHT and EC_PWM_TYPE_KB_LIGHT pwm
> > > types to the PWM cros_ec_pwm driver. This allows specifying one of these
> > > PWM channel by functionality, and let the EC firmware pick the correct
> > > channel, thus abstracting the hardware implementation from the kernel
> > > driver.
> > >
> > > To use it, define the node with the "google,cros-ec-pwm-type"
> > > compatible.
> > >
> > > Signed-off-by: Fabio Baltieri <fabiobaltieri@...omium.org>
> > > Reviewed-by: Tzung-Bi Shih <tzungbi@...nel.org>
> > > ---
> > >  drivers/pwm/pwm-cros-ec.c | 82 ++++++++++++++++++++++++++++++++-------
> > >  1 file changed, 67 insertions(+), 15 deletions(-)
> > >
> > > diff --git a/drivers/pwm/pwm-cros-ec.c b/drivers/pwm/pwm-cros-ec.c
> > > index 5e29d9c682c3..7f10f56c3eb6 100644
> > > --- a/drivers/pwm/pwm-cros-ec.c
> > > +++ b/drivers/pwm/pwm-cros-ec.c
> > > @@ -12,17 +12,21 @@
> > >  #include <linux/pwm.h>
> > >  #include <linux/slab.h>
> > >
> > > +#include <dt-bindings/mfd/cros_ec.h>
> > > +
> > >  /**
> > >   * struct cros_ec_pwm_device - Driver data for EC PWM
> > >   *
> > >   * @dev: Device node
> > >   * @ec: Pointer to EC device
> > >   * @chip: PWM controller chip
> > > + * @use_pwm_type: Use PWM types instead of generic channels
> > >   */
> > >  struct cros_ec_pwm_device {
> > >     struct device *dev;
> > >     struct cros_ec_device *ec;
> > >     struct pwm_chip chip;
> > > +   bool use_pwm_type;
> > >  };
> > >
> > >  /**
> > > @@ -58,14 +62,31 @@ static void cros_ec_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
> > >     kfree(channel);
> > >  }
> > >
> > > -static int cros_ec_pwm_set_duty(struct cros_ec_device *ec, u8 index, u16 duty)
> > > +static int cros_ec_dt_type_to_pwm_type(u8 dt_index, u8 *pwm_type)
> > >  {
> > > +   switch (dt_index) {
> > > +   case CROS_EC_PWM_DT_KB_LIGHT:
> > > +           *pwm_type = EC_PWM_TYPE_KB_LIGHT;
> > > +           return 0;
> > > +   case CROS_EC_PWM_DT_DISPLAY_LIGHT:
> > > +           *pwm_type = EC_PWM_TYPE_DISPLAY_LIGHT;
> > > +           return 0;
> > > +   default:
> > > +           return -EINVAL;
> > > +   }
> > > +}
> > > +
> > > +static int cros_ec_pwm_set_duty(struct cros_ec_pwm_device *ec_pwm, u8 index,
> > > +                           u16 duty)
> > > +{
> > > +   struct cros_ec_device *ec = ec_pwm->ec;
> > >     struct {
> > >             struct cros_ec_command msg;
> > >             struct ec_params_pwm_set_duty params;
> > >     } __packed buf;
> > >     struct ec_params_pwm_set_duty *params = &buf.params;
> > >     struct cros_ec_command *msg = &buf.msg;
> > > +   int ret;
> > >
> > >     memset(&buf, 0, sizeof(buf));
> > >
> > > @@ -75,14 +96,25 @@ static int cros_ec_pwm_set_duty(struct cros_ec_device *ec, u8 index, u16 duty)
> > >     msg->outsize = sizeof(*params);
> > >
> > >     params->duty = duty;
> > > -   params->pwm_type = EC_PWM_TYPE_GENERIC;
> > > -   params->index = index;
> > > +
> > > +   if (ec_pwm->use_pwm_type) {
> > > +           ret = cros_ec_dt_type_to_pwm_type(index, &params->pwm_type);
> > > +           if (ret) {
> > > +                   dev_err(ec->dev, "Invalid PWM type index: %d\n", index);
> > > +                   return ret;
> > > +           }
> > > +           params->index = 0;
> > > +   } else {
> > > +           params->pwm_type = EC_PWM_TYPE_GENERIC;
> > > +           params->index = index;
> > > +   }
> > >
> > >     return cros_ec_cmd_xfer_status(ec, msg);
> > >  }
> > >
> > > -static int cros_ec_pwm_get_duty(struct cros_ec_device *ec, u8 index)
> > > +static int cros_ec_pwm_get_duty(struct cros_ec_pwm_device *ec_pwm, u8 index)
> > >  {
> > > +   struct cros_ec_device *ec = ec_pwm->ec;
> > >     struct {
> > >             struct cros_ec_command msg;
> > >             union {
> > > @@ -102,8 +134,17 @@ static int cros_ec_pwm_get_duty(struct cros_ec_device *ec, u8 index)
> > >     msg->insize = sizeof(*resp);
> > >     msg->outsize = sizeof(*params);
> > >
> > > -   params->pwm_type = EC_PWM_TYPE_GENERIC;
> > > -   params->index = index;
> > > +   if (ec_pwm->use_pwm_type) {
> > > +           ret = cros_ec_dt_type_to_pwm_type(index, &params->pwm_type);
> > > +           if (ret) {
> > > +                   dev_err(ec->dev, "Invalid PWM type index: %d\n", index);
> > > +                   return ret;
> > > +           }
> > > +           params->index = 0;
> > > +   } else {
> > > +           params->pwm_type = EC_PWM_TYPE_GENERIC;
> > > +           params->index = index;
> > > +   }
> > >
> > >     ret = cros_ec_cmd_xfer_status(ec, msg);
> > >     if (ret < 0)
> > > @@ -133,7 +174,7 @@ static int cros_ec_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> > >      */
> > >     duty_cycle = state->enabled ? state->duty_cycle : 0;
> > >
> > > -   ret = cros_ec_pwm_set_duty(ec_pwm->ec, pwm->hwpwm, duty_cycle);
> > > +   ret = cros_ec_pwm_set_duty(ec_pwm, pwm->hwpwm, duty_cycle);
> > >     if (ret < 0)
> > >             return ret;
> > >
> > > @@ -149,7 +190,7 @@ static void cros_ec_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> > >     struct cros_ec_pwm *channel = pwm_get_chip_data(pwm);
> > >     int ret;
> > >
> > > -   ret = cros_ec_pwm_get_duty(ec_pwm->ec, pwm->hwpwm);
> > > +   ret = cros_ec_pwm_get_duty(ec_pwm, pwm->hwpwm);
> > >     if (ret < 0) {
> > >             dev_err(chip->dev, "error getting initial duty: %d\n", ret);
> > >             return;
> > > @@ -204,13 +245,13 @@ static const struct pwm_ops cros_ec_pwm_ops = {
> > >   * of PWMs it supports directly, so we have to read the pwm duty cycle for
> > >   * subsequent channels until we get an error.
> > >   */
> > > -static int cros_ec_num_pwms(struct cros_ec_device *ec)
> > > +static int cros_ec_num_pwms(struct cros_ec_pwm_device *ec_pwm)
> > >  {
> > >     int i, ret;
> > >
> > >     /* The index field is only 8 bits */
> > >     for (i = 0; i <= U8_MAX; i++) {
> > > -           ret = cros_ec_pwm_get_duty(ec, i);
> > > +           ret = cros_ec_pwm_get_duty(ec_pwm, i);
> > >             /*
> > >              * We look for SUCCESS, INVALID_COMMAND, or INVALID_PARAM
> > >              * responses; everything else is treated as an error.
> > > @@ -236,6 +277,7 @@ static int cros_ec_pwm_probe(struct platform_device *pdev)
> > >  {
> > >     struct cros_ec_device *ec = dev_get_drvdata(pdev->dev.parent);
> > >     struct device *dev = &pdev->dev;
> > > +   struct device_node *np = pdev->dev.of_node;
> > >     struct cros_ec_pwm_device *ec_pwm;
> > >     struct pwm_chip *chip;
> > >     int ret;
> > > @@ -251,17 +293,26 @@ static int cros_ec_pwm_probe(struct platform_device *pdev)
> > >     chip = &ec_pwm->chip;
> > >     ec_pwm->ec = ec;
> > >
> > > +   if (of_device_is_compatible(np, "google,cros-ec-pwm-type"))
> > > +           ec_pwm->use_pwm_type = true;
> >
> > Isn't it possible to just use an optional boolean property
> > (for example: "use-pwm-type") instead of defining a new compatible
> > string?
>
> Yeah that's what I did originally but Rob suggested to use a new
> compatible instead:
>
> https://lore.kernel.org/chrome-platform/Yk20uTE%2FVdm2c6jI@robh.at.kernel.org/

Thanks for the context. I suppose one could use the "split number
space" suggestion mentioned there,
and still be able to supply the right arguments for
pwm_request_from_chip() (since we're the ones
supplying the argument via of_xlate). But, if the DT maintainer is
alright with a new compatible, then
of course you should go with whatever works for you.

>
> > > +
> > >     /* PWM chip */
> > >     chip->dev = dev;
> > >     chip->ops = &cros_ec_pwm_ops;
> > >     chip->of_xlate = cros_ec_pwm_xlate;
> > >     chip->of_pwm_n_cells = 1;
> > > -   ret = cros_ec_num_pwms(ec);
> > > -   if (ret < 0) {
> > > -           dev_err(dev, "Couldn't find PWMs: %d\n", ret);
> > > -           return ret;
> > > +
> > > +   if (ec_pwm->use_pwm_type) {
> > > +           chip->npwm = CROS_EC_PWM_DT_COUNT;
> > > +   } else {
> > > +           ret = cros_ec_num_pwms(ec_pwm);
> > > +           if (ret < 0) {
> > > +                   dev_err(dev, "Couldn't find PWMs: %d\n", ret);
> > > +                   return ret;
> > > +           }
> > > +           chip->npwm = ret;
> > >     }
> > > -   chip->npwm = ret;
> > > +
> > >     dev_dbg(dev, "Probed %u PWMs\n", chip->npwm);
> > >
> > >     ret = pwmchip_add(chip);
> > > @@ -288,6 +339,7 @@ static int cros_ec_pwm_remove(struct platform_device *dev)
> > >  #ifdef CONFIG_OF
> > >  static const struct of_device_id cros_ec_pwm_of_match[] = {
> > >     { .compatible = "google,cros-ec-pwm" },
> > > +   { .compatible = "google,cros-ec-pwm-type" },
> > >     {},
> > >  };
> > >  MODULE_DEVICE_TABLE(of, cros_ec_pwm_of_match);
> > > --
> > > 2.36.0.rc0.470.gd361397f0d-goog
> > >
> > >
>
> --
> Fabio Baltieri

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