Re: [PATCH] pwm: ftm: fix clock enable/disable when using PM

[Stefan Agner]

Hi Thierry,

On 2015-05-29 22:48, Stefan Agner wrote:
> The driver has multiple issues when enabling/disabling clocks. A given
> instance enables/disables three clocks: the bus clock, the counter
> clock and the PWM clock. The bus clock gets enabled on pwm_request,
> whereas the counter and PWM clocks will be enabled upon pwm_enable.
> 
> When entering suspend, the current behavior relies on the FTM_OUTMASK
> register: If a PWM output is unmasked, the driver assumes the clocks
> are enabled. However, some PWM instances, e.g. Vybrid's FTM1, only
> have 2 channels connected. In that case, the FTM_OUTMASK reads only
> 0x3, even when it was initialized with 0xff. Hence for those PWM
> instances, the current approach does not work at all.
> 
> A second issue is that the three clocks are not treated differently
> regarding PWM's enabled/requested state. This can lead to clocks
> getting disabled which have not been enabled in the first place (a PWM
> channel which only has been requested).
> 
> A third issue applies to the bus clock only, which can get enabled
> multiple times (once for each PWM channel of a PWM chip). This is
> fine, however when entering suspend mode, the clock only gets disabled
> once.
> 
> To fix the issues this change introduces a different approach by
> relying on the enable/prepared counters of the clock framework. Clocks
> get disabled during suspend and back enabled on resume regarding to
> the PWM channels individual state. However, since we do not count the
> clocks locally, this change no longer clears the Status and Control
> registers Clock Source Selection (FTM_SC[CLKS]). There have not
> observed issues with that approach so far.


Any comment on that?

--
Stefan

> 
> Signed-off-by: Stefan Agner <stefan@xxxxxxxx>
> ---
>  drivers/pwm/pwm-fsl-ftm.c | 58 ++++++++++++++++++++---------------------------
>  1 file changed, 25 insertions(+), 33 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-fsl-ftm.c b/drivers/pwm/pwm-fsl-ftm.c
> index f9dfc8b..5e1dd96 100644
> --- a/drivers/pwm/pwm-fsl-ftm.c
> +++ b/drivers/pwm/pwm-fsl-ftm.c
> @@ -80,7 +80,6 @@ struct fsl_pwm_chip {
>  
>  	struct mutex lock;
>  
> -	unsigned int use_count;
>  	unsigned int cnt_select;
>  	unsigned int clk_ps;
>  
> @@ -300,9 +299,6 @@ static int fsl_counter_clock_enable(struct
> fsl_pwm_chip *fpc)
>  {
>  	int ret;
>  
> -	if (fpc->use_count++ != 0)
> -		return 0;
> -
>  	/* select counter clock source */
>  	regmap_update_bits(fpc->regmap, FTM_SC, FTM_SC_CLK_MASK,
>  			   FTM_SC_CLK(fpc->cnt_select));
> @@ -334,25 +330,6 @@ static int fsl_pwm_enable(struct pwm_chip *chip,
> struct pwm_device *pwm)
>  	return ret;
>  }
>  
> -static void fsl_counter_clock_disable(struct fsl_pwm_chip *fpc)
> -{
> -	/*
> -	 * already disabled, do nothing
> -	 */
> -	if (fpc->use_count == 0)
> -		return;
> -
> -	/* there are still users, so can't disable yet */
> -	if (--fpc->use_count > 0)
> -		return;
> -
> -	/* no users left, disable PWM counter clock */
> -	regmap_update_bits(fpc->regmap, FTM_SC, FTM_SC_CLK_MASK, 0);
> -
> -	clk_disable_unprepare(fpc->clk[FSL_PWM_CLK_CNTEN]);
> -	clk_disable_unprepare(fpc->clk[fpc->cnt_select]);
> -}
> -
>  static void fsl_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
>  {
>  	struct fsl_pwm_chip *fpc = to_fsl_chip(chip);
> @@ -362,7 +339,8 @@ static void fsl_pwm_disable(struct pwm_chip *chip,
> struct pwm_device *pwm)
>  	regmap_update_bits(fpc->regmap, FTM_OUTMASK, BIT(pwm->hwpwm),
>  			   BIT(pwm->hwpwm));
>  
> -	fsl_counter_clock_disable(fpc);
> +	clk_disable_unprepare(fpc->clk[FSL_PWM_CLK_CNTEN]);
> +	clk_disable_unprepare(fpc->clk[fpc->cnt_select]);
>  
>  	regmap_read(fpc->regmap, FTM_OUTMASK, &val);
>  	if ((val & 0xFF) == 0xFF)
> @@ -492,17 +470,24 @@ static int fsl_pwm_remove(struct platform_device *pdev)
>  static int fsl_pwm_suspend(struct device *dev)
>  {
>  	struct fsl_pwm_chip *fpc = dev_get_drvdata(dev);
> -	u32 val;
> +	int i;
>  
>  	regcache_cache_only(fpc->regmap, true);
>  	regcache_mark_dirty(fpc->regmap);
>  
> -	/* read from cache */
> -	regmap_read(fpc->regmap, FTM_OUTMASK, &val);
> -	if ((val & 0xFF) != 0xFF) {
> +	for (i = 0; i < fpc->chip.npwm; i++) {
> +		struct pwm_device *pwm = &fpc->chip.pwms[i];
> +
> +		if (!test_bit(PWMF_REQUESTED, &pwm->flags))
> +			continue;
> +
> +		clk_disable_unprepare(fpc->clk[FSL_PWM_CLK_SYS]);
> +
> +		if (!test_bit(PWMF_ENABLED, &pwm->flags))
> +			continue;
> +
>  		clk_disable_unprepare(fpc->clk[FSL_PWM_CLK_CNTEN]);
>  		clk_disable_unprepare(fpc->clk[fpc->cnt_select]);
> -		clk_disable_unprepare(fpc->clk[FSL_PWM_CLK_SYS]);
>  	}
>  
>  	return 0;
> @@ -511,12 +496,19 @@ static int fsl_pwm_suspend(struct device *dev)
>  static int fsl_pwm_resume(struct device *dev)
>  {
>  	struct fsl_pwm_chip *fpc = dev_get_drvdata(dev);
> -	u32 val;
> +	int i;
> +
> +	for (i = 0; i < fpc->chip.npwm; i++) {
> +		struct pwm_device *pwm = &fpc->chip.pwms[i];
> +
> +		if (!test_bit(PWMF_REQUESTED, &pwm->flags))
> +			continue;
>  
> -	/* read from cache */
> -	regmap_read(fpc->regmap, FTM_OUTMASK, &val);
> -	if ((val & 0xFF) != 0xFF) {
>  		clk_prepare_enable(fpc->clk[FSL_PWM_CLK_SYS]);
> +
> +		if (!test_bit(PWMF_ENABLED, &pwm->flags))
> +			continue;
> +
>  		clk_prepare_enable(fpc->clk[fpc->cnt_select]);
>  		clk_prepare_enable(fpc->clk[FSL_PWM_CLK_CNTEN]);
>  	}

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