Re: [PATCH] clk: qcom: gdsc: Fix handling of hw control enable/disable

[Stanimir Varbanov]

Hi Rajendra,

Thanks for the patch!

On 01/10/2017 07:54 AM, Rajendra Nayak wrote:
> Once a gdsc is brought in and out of HW control, there is a
> power down and up cycle which can take upto 1us. Polling on
> the gdsc status immediately after the hw control enable/disable
> can mislead software/firmware to belive the gdsc is already either on
> or off, while its yet to complete the power cycle.
> To avoid this add a 1us delay post a enable/disable of HW control
> mode.
> 
> Also after the HW control mode is disabled, poll on the status to
> check gdsc status reflects its 'on' before force disabling it
> in software.
> 
> Reported-by: Stanimir Varbanov <stanimir.varbanov@xxxxxxxxxx>
> Signed-off-by: Rajendra Nayak <rnayak@xxxxxxxxxxxxxx>
> ---
> 
> Stan,
> If there was a specific issue you saw with venus because of the missing
> delay and poll, can you check if this fixes any of that.
> 
>  drivers/clk/qcom/gdsc.c | 58 ++++++++++++++++++++++++++++++++++++++-----------
>  1 file changed, 45 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/clk/qcom/gdsc.c b/drivers/clk/qcom/gdsc.c
> index 288186c..6fbd6df 100644
> --- a/drivers/clk/qcom/gdsc.c
> +++ b/drivers/clk/qcom/gdsc.c
> @@ -63,11 +63,26 @@ static int gdsc_hwctrl(struct gdsc *sc, bool en)
>  	return regmap_update_bits(sc->regmap, sc->gdscr, HW_CONTROL_MASK, val);
>  }
>  
> +static int gdsc_poll_status(struct gdsc *sc, unsigned int reg, bool val)

Could you rename 'val' to 'en'.

> +{
> +	ktime_t start;
> +
> +	start = ktime_get();
> +	do {
> +		if (gdsc_is_enabled(sc, reg) == val)
> +			return 0;
> +	} while (ktime_us_delta(ktime_get(), start) < TIMEOUT_US);
> +
> +	if (gdsc_is_enabled(sc, reg) == val)
> +		return 0;
> +
> +	return -ETIMEDOUT;
> +}
> +
>  static int gdsc_toggle_logic(struct gdsc *sc, bool en)
>  {
>  	int ret;
>  	u32 val = en ? 0 : SW_COLLAPSE_MASK;
> -	ktime_t start;
>  	unsigned int status_reg = sc->gdscr;
>  
>  	ret = regmap_update_bits(sc->regmap, sc->gdscr, SW_COLLAPSE_MASK, val);
> @@ -100,16 +115,7 @@ static int gdsc_toggle_logic(struct gdsc *sc, bool en)
>  		udelay(1);
>  	}
>  
> -	start = ktime_get();
> -	do {
> -		if (gdsc_is_enabled(sc, status_reg) == en)
> -			return 0;
> -	} while (ktime_us_delta(ktime_get(), start) < TIMEOUT_US);
> -
> -	if (gdsc_is_enabled(sc, status_reg) == en)
> -		return 0;
> -
> -	return -ETIMEDOUT;
> +	return gdsc_poll_status(sc, status_reg, en);
>  }
>  
>  static inline int gdsc_deassert_reset(struct gdsc *sc)
> @@ -188,8 +194,19 @@ static int gdsc_enable(struct generic_pm_domain *domain)
>  	udelay(1);
>  
>  	/* Turn on HW trigger mode if supported */
> -	if (sc->flags & HW_CTRL)
> -		return gdsc_hwctrl(sc, true);
> +	if (sc->flags & HW_CTRL) {
> +		ret = gdsc_hwctrl(sc, true);
> +		/*
> +		 * Wait for the GDSC to go through a power down and
> +		 * up cycle.  In case a firmware ends up polling status
> +		 * bits for the gdsc, it might read an 'on' status before
> +		 * the GDSC can finish the power cycle.
> +		 * We wait 1us before returning to ensure the firmware
> +		 * can't immediately poll the status bits.
> +		 */
> +		mb();

Missing comment for this memory barrier, although I think it is
pointless because regmap-mmio using readl and writel.


> +		udelay(1);
> +	}
>  
>  	return 0;
>  }
> @@ -204,9 +221,24 @@ static int gdsc_disable(struct generic_pm_domain *domain)
>  
>  	/* Turn off HW trigger mode if supported */
>  	if (sc->flags & HW_CTRL) {
> +		unsigned int reg;
> +
>  		ret = gdsc_hwctrl(sc, false);
>  		if (ret < 0)
>  			return ret;
> +		/*
> +		 * Wait for the GDSC to go through a power down and
> +		 * up cycle.  In case we end up polling status
> +		 * bits for the gdsc before the power cycle is completed
> +		 * it might read an 'on' status wrongly.
> +		 */
> +		mb();

Same comment as above one.

> +		udelay(1);
> +
> +		reg = sc->gds_hw_ctrl ? sc->gds_hw_ctrl : sc->gdscr;
> +		ret = gdsc_poll_status(sc, reg, 0);

This should be gdsc_poll_status(sc, reg, true) because after disabling
hw_control we expect that the GDSC is in power_on state.

> +		if (ret)
> +			return ret;
>  	}
>  
>  	if (sc->pwrsts & PWRSTS_OFF)
> 

-- 
regards,
Stan