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Date:   Tue, 22 Feb 2022 14:49:09 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Song Chen <chensong_2000@189.cn>
Cc:     johan@kernel.org, elder@kernel.org, thierry.reding@gmail.com,
        u.kleine-koenig@pengutronix.de, lee.jones@linaro.org,
        greybus-dev@lists.linaro.org, linux-staging@lists.linux.dev,
        linux-kernel@vger.kernel.org, linux-pwm@vger.kernel.org
Subject: Re: [PATCH v2] staging: greybus: introduce pwm_ops::apply
Message-ID: <YhTp1RAXDZrA5QKK@kroah.com>
References: <1644580947-8529-1-git-send-email-chensong_2000@189.cn>
 <YhPGqg2BydlAFiM1@kroah.com>
 <ccbddd00-a2d6-c613-bc7b-e08d7fa2306b@189.cn>
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On Tue, Feb 22, 2022 at 02:19:12PM +0800, Song Chen wrote:
> Hi Greg,
> 
> 在 2022/2/22 01:06, Greg KH 写道:
> > On Fri, Feb 11, 2022 at 08:02:27PM +0800, Song Chen wrote:
> > > Introduce apply in pwm_ops to replace legacy operations,
> > > like enable, disable, config and set_polarity.
> > > 
> > > Signed-off-by: Song Chen <chensong_2000@189.cn>
> > > 
> > > ---
> > > V2:
> > > 1, define duty_cycle and period as u64 in gb_pwm_config_operation.
> > > 2, define duty and period as u64 in gb_pwm_config_request.
> > > 3, disable before configuring duty and period if the eventual goal
> > >     is a disabled state.
> > > ---
> > >   drivers/staging/greybus/pwm.c             | 61 ++++++++++++-----------
> > >   include/linux/greybus/greybus_protocols.h |  4 +-
> > >   2 files changed, 34 insertions(+), 31 deletions(-)
> > > 
> > > diff --git a/drivers/staging/greybus/pwm.c b/drivers/staging/greybus/pwm.c
> > > index 891a6a672378..03c69db5b9be 100644
> > > --- a/drivers/staging/greybus/pwm.c
> > > +++ b/drivers/staging/greybus/pwm.c
> > > @@ -89,7 +89,7 @@ static int gb_pwm_deactivate_operation(struct gb_pwm_chip *pwmc,
> > >   }
> > >   static int gb_pwm_config_operation(struct gb_pwm_chip *pwmc,
> > > -				   u8 which, u32 duty, u32 period)
> > > +				   u8 which, u64 duty, u64 period)
> > >   {
> > >   	struct gb_pwm_config_request request;
> > >   	struct gbphy_device *gbphy_dev;
> > > @@ -99,8 +99,8 @@ static int gb_pwm_config_operation(struct gb_pwm_chip *pwmc,
> > >   		return -EINVAL;
> > >   	request.which = which;
> > > -	request.duty = cpu_to_le32(duty);
> > > -	request.period = cpu_to_le32(period);
> > > +	request.duty = duty;
> > > +	request.period = period;
> > >   	gbphy_dev = to_gbphy_dev(pwmc->chip.dev);
> > >   	ret = gbphy_runtime_get_sync(gbphy_dev);
> > > @@ -204,43 +204,46 @@ static void gb_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
> > >   	gb_pwm_deactivate_operation(pwmc, pwm->hwpwm);
> > >   }
> > > -static int gb_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> > > -			 int duty_ns, int period_ns)
> > > +static int gb_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> > > +			const struct pwm_state *state)
> > >   {
> > > +	int err;
> > > +	bool enabled = pwm->state.enabled;
> > >   	struct gb_pwm_chip *pwmc = pwm_chip_to_gb_pwm_chip(chip);
> > > -	return gb_pwm_config_operation(pwmc, pwm->hwpwm, duty_ns, period_ns);
> > > -};
> > > -
> > > -static int gb_pwm_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm,
> > > -			       enum pwm_polarity polarity)
> > > -{
> > > -	struct gb_pwm_chip *pwmc = pwm_chip_to_gb_pwm_chip(chip);
> > > -
> > > -	return gb_pwm_set_polarity_operation(pwmc, pwm->hwpwm, polarity);
> > > -};
> > > +	/* set polarity */
> > > +	if (state->polarity != pwm->state.polarity) {
> > > +		if (enabled) {
> > > +			gb_pwm_disable_operation(pwmc, pwm->hwpwm);
> > > +			enabled = false;
> > > +		}
> > > +		err = gb_pwm_set_polarity_operation(pwmc, pwm->hwpwm, state->polarity);
> > > +		if (err)
> > > +			return err;
> > > +	}
> > > -static int gb_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
> > > -{
> > > -	struct gb_pwm_chip *pwmc = pwm_chip_to_gb_pwm_chip(chip);
> > > +	if (!state->enabled) {
> > > +		if (enabled)
> > > +			gb_pwm_disable_operation(pwmc, pwm->hwpwm);
> > > +		return 0;
> > > +	}
> > > -	return gb_pwm_enable_operation(pwmc, pwm->hwpwm);
> > > -};
> > > +	/* set period and duty cycle*/
> > > +	err = gb_pwm_config_operation(pwmc, pwm->hwpwm, state->duty_cycle, state->period);
> > > +	if (err)
> > > +		return err;
> > > -static void gb_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
> > > -{
> > > -	struct gb_pwm_chip *pwmc = pwm_chip_to_gb_pwm_chip(chip);
> > > +	/* enable/disable */
> > > +	if (!enabled)
> > > +		return gb_pwm_enable_operation(pwmc, pwm->hwpwm);
> > > -	gb_pwm_disable_operation(pwmc, pwm->hwpwm);
> > > -};
> > > +	return 0;
> > > +}
> > >   static const struct pwm_ops gb_pwm_ops = {
> > >   	.request = gb_pwm_request,
> > >   	.free = gb_pwm_free,
> > > -	.config = gb_pwm_config,
> > > -	.set_polarity = gb_pwm_set_polarity,
> > > -	.enable = gb_pwm_enable,
> > > -	.disable = gb_pwm_disable,
> > > +	.apply = gb_pwm_apply,
> > >   	.owner = THIS_MODULE,
> > >   };
> > > diff --git a/include/linux/greybus/greybus_protocols.h b/include/linux/greybus/greybus_protocols.h
> > > index aeb8f9243545..81a6f16de098 100644
> > > --- a/include/linux/greybus/greybus_protocols.h
> > > +++ b/include/linux/greybus/greybus_protocols.h
> > > @@ -812,8 +812,8 @@ struct gb_pwm_deactivate_request {
> > >   struct gb_pwm_config_request {
> > >   	__u8	which;
> > > -	__le32	duty;
> > > -	__le32	period;
> > > +	__u64	duty;
> > > +	__u64	period;
> > >   } __packed;
> > 
> > Did you just change a greybus protocol message that is sent over the
> > wire?  Why?  And why drop the endian marking of it?
> 
> I discussed with Uwe about losing bit and found there is no perfect way to
> avoid, even in Uwe's patch[1], as a result, we decided to widen duty and
> period in gb_pwm_config_request, the other side of the wire is supposed to
> change accordingly to support 64bit duty and period too(this will introduce
> compatibility problem and there is no variable like version to address it),
> similar with ktime_t in y2038, below is the detail [2]

Where are you changing the "other side of the wire" here?  That wire is
in firmware, how are you going to coordinate that change?

This is a hardware API, you can not change it without a lot of very
careful work, and I still do not understand why it is needed.  What
"problem" is this solving that requires the protocol to change?

thanks,

greg k-h