[PATCH v2] leds: qcom-lpg: Fix PWM period limits

[PATCH v2] leds: qcom-lpg: Fix PWM period limits

[Bjorn Andersson]

The introduction of high resolution PWM support changed the order of the
operations in the calculation of min and max period. The result in both
divisions is in most cases a truncation to 0, which limits the period to
the range of [0, 0].

Both numerators (and denominators) are within 64 bits, so the whole
expression can be put directly into the div64_u64, instead of doing it
partially.

Fixes: b00d2ed37617 ("leds: rgb: leds-qcom-lpg: Add support for high resolution PWM")
Reviewed-by: Caleb Connolly <caleb.connolly@linaro.org>
Tested-by: Steev Klimaszewski <steev@kali.org>
Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>
---

Changes since v1:
- Reworded first sentence to express that it's the order and not the
  previously non-existent parenthesis that changed...
- Picked up review tags.

 drivers/leds/rgb/leds-qcom-lpg.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/leds/rgb/leds-qcom-lpg.c b/drivers/leds/rgb/leds-qcom-lpg.c
index c9cea797a697..7287fadc00df 100644
--- a/drivers/leds/rgb/leds-qcom-lpg.c
+++ b/drivers/leds/rgb/leds-qcom-lpg.c
@@ -312,14 +312,14 @@ static int lpg_calc_freq(struct lpg_channel *chan, uint64_t period)
 		max_res = LPG_RESOLUTION_9BIT;
 	}
 
-	min_period = (u64)NSEC_PER_SEC *
-			div64_u64((1 << pwm_resolution_arr[0]), clk_rate_arr[clk_len - 1]);
+	min_period = div64_u64((u64)NSEC_PER_SEC * (1 << pwm_resolution_arr[0]),
+			       clk_rate_arr[clk_len - 1]);
 	if (period <= min_period)
 		return -EINVAL;
 
 	/* Limit period to largest possible value, to avoid overflows */
-	max_period = (u64)NSEC_PER_SEC * max_res * LPG_MAX_PREDIV *
-			div64_u64((1 << LPG_MAX_M), 1024);
+	max_period = div64_u64((u64)NSEC_PER_SEC * max_res * LPG_MAX_PREDIV * (1 << LPG_MAX_M),
+			       1024);
 	if (period > max_period)
 		period = max_period;
 
-- 
2.25.1

Re: [PATCH v2] leds: qcom-lpg: Fix PWM period limits

[Johan Hovold]

On Mon, May 15, 2023 at 09:26:04AM -0700, Bjorn Andersson wrote:
> The introduction of high resolution PWM support changed the order of the
> operations in the calculation of min and max period. The result in both
> divisions is in most cases a truncation to 0, which limits the period to
> the range of [0, 0].
> 
> Both numerators (and denominators) are within 64 bits, so the whole
> expression can be put directly into the div64_u64, instead of doing it
> partially.
> 
> Fixes: b00d2ed37617 ("leds: rgb: leds-qcom-lpg: Add support for high resolution PWM")
> Reviewed-by: Caleb Connolly <caleb.connolly@linaro.org>
> Tested-by: Steev Klimaszewski <steev@kali.org>
> Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>

Tested-by: Johan Hovold <johan+linaro@kernel.org>

Pavel or Lee, could you pick this one up for 6.4 as it fixes a
regression (e.g. broken backlight on a number of laptops like the X13s)?

> ---
> 
> Changes since v1:
> - Reworded first sentence to express that it's the order and not the
>   previously non-existent parenthesis that changed...
> - Picked up review tags.
> 
>  drivers/leds/rgb/leds-qcom-lpg.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/leds/rgb/leds-qcom-lpg.c b/drivers/leds/rgb/leds-qcom-lpg.c
> index c9cea797a697..7287fadc00df 100644
> --- a/drivers/leds/rgb/leds-qcom-lpg.c
> +++ b/drivers/leds/rgb/leds-qcom-lpg.c
> @@ -312,14 +312,14 @@ static int lpg_calc_freq(struct lpg_channel *chan, uint64_t period)
>  		max_res = LPG_RESOLUTION_9BIT;
>  	}
>  
> -	min_period = (u64)NSEC_PER_SEC *
> -			div64_u64((1 << pwm_resolution_arr[0]), clk_rate_arr[clk_len - 1]);
> +	min_period = div64_u64((u64)NSEC_PER_SEC * (1 << pwm_resolution_arr[0]),
> +			       clk_rate_arr[clk_len - 1]);
>  	if (period <= min_period)
>  		return -EINVAL;
>  
>  	/* Limit period to largest possible value, to avoid overflows */
> -	max_period = (u64)NSEC_PER_SEC * max_res * LPG_MAX_PREDIV *
> -			div64_u64((1 << LPG_MAX_M), 1024);
> +	max_period = div64_u64((u64)NSEC_PER_SEC * max_res * LPG_MAX_PREDIV * (1 << LPG_MAX_M),
> +			       1024);
>  	if (period > max_period)
>  		period = max_period;

Johan

Re: [PATCH v2] leds: qcom-lpg: Fix PWM period limits

[Lee Jones]

On Wed, 24 May 2023, Johan Hovold wrote:

> On Mon, May 15, 2023 at 09:26:04AM -0700, Bjorn Andersson wrote:
> > The introduction of high resolution PWM support changed the order of the
> > operations in the calculation of min and max period. The result in both
> > divisions is in most cases a truncation to 0, which limits the period to
> > the range of [0, 0].
> > 
> > Both numerators (and denominators) are within 64 bits, so the whole
> > expression can be put directly into the div64_u64, instead of doing it
> > partially.
> > 
> > Fixes: b00d2ed37617 ("leds: rgb: leds-qcom-lpg: Add support for high resolution PWM")
> > Reviewed-by: Caleb Connolly <caleb.connolly@linaro.org>
> > Tested-by: Steev Klimaszewski <steev@kali.org>
> > Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>
> 
> Tested-by: Johan Hovold <johan+linaro@kernel.org>
> 
> Pavel or Lee, could you pick this one up for 6.4 as it fixes a
> regression (e.g. broken backlight on a number of laptops like the X13s)?

I don't presently have any plans for a -fixes submission.

If anyone else would like to submit it, please be my guest:

Acked-by: Lee Jones <lee@kernel.org>

-- 
Lee Jones [李琼斯]

Re: [PATCH v2] leds: qcom-lpg: Fix PWM period limits

[Johan Hovold]

On Fri, Jun 02, 2023 at 10:19:28AM +0100, Lee Jones wrote:
> On Wed, 24 May 2023, Johan Hovold wrote:

> > Pavel or Lee, could you pick this one up for 6.4 as it fixes a
> > regression (e.g. broken backlight on a number of laptops like the X13s)?
> 
> I don't presently have any plans for a -fixes submission.
> 
> If anyone else would like to submit it, please be my guest:
> 
> Acked-by: Lee Jones <lee@kernel.org>

That was not the answer I expected, but sure, I've sent it on to Linus:

	https://lore.kernel.org/lkml/ZHte5sPkB6-D-94G@hovoldconsulting.com/

Johan

Re: [PATCH v2] leds: qcom-lpg: Fix PWM period limits

[Lee Jones]

On Sat, 03 Jun 2023, Johan Hovold wrote:

> On Fri, Jun 02, 2023 at 10:19:28AM +0100, Lee Jones wrote:
> > On Wed, 24 May 2023, Johan Hovold wrote:
> 
> > > Pavel or Lee, could you pick this one up for 6.4 as it fixes a
> > > regression (e.g. broken backlight on a number of laptops like the X13s)?
> > 
> > I don't presently have any plans for a -fixes submission.
> > 
> > If anyone else would like to submit it, please be my guest:
> > 
> > Acked-by: Lee Jones <lee@kernel.org>
> 
> That was not the answer I expected, but sure, I've sent it on to Linus:

Sorry, soooo busy right now.  Trying not to drop too many plates.

> 	https://lore.kernel.org/lkml/ZHte5sPkB6-D-94G@hovoldconsulting.com/

*fist bump*

-- 
Lee Jones [李琼斯]

Re: [PATCH v2] leds: qcom-lpg: Fix PWM period limits

[Neil Armstrong]

On 15/05/2023 18:26, Bjorn Andersson wrote:
> The introduction of high resolution PWM support changed the order of the
> operations in the calculation of min and max period. The result in both
> divisions is in most cases a truncation to 0, which limits the period to
> the range of [0, 0].
> 
> Both numerators (and denominators) are within 64 bits, so the whole
> expression can be put directly into the div64_u64, instead of doing it
> partially.
> 
> Fixes: b00d2ed37617 ("leds: rgb: leds-qcom-lpg: Add support for high resolution PWM")
> Reviewed-by: Caleb Connolly <caleb.connolly@linaro.org>
> Tested-by: Steev Klimaszewski <steev@kali.org>
> Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>
> ---
> 
> Changes since v1:
> - Reworded first sentence to express that it's the order and not the
>    previously non-existent parenthesis that changed...
> - Picked up review tags.
> 
>   drivers/leds/rgb/leds-qcom-lpg.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/leds/rgb/leds-qcom-lpg.c b/drivers/leds/rgb/leds-qcom-lpg.c
> index c9cea797a697..7287fadc00df 100644
> --- a/drivers/leds/rgb/leds-qcom-lpg.c
> +++ b/drivers/leds/rgb/leds-qcom-lpg.c
> @@ -312,14 +312,14 @@ static int lpg_calc_freq(struct lpg_channel *chan, uint64_t period)
>   		max_res = LPG_RESOLUTION_9BIT;
>   	}
>   
> -	min_period = (u64)NSEC_PER_SEC *
> -			div64_u64((1 << pwm_resolution_arr[0]), clk_rate_arr[clk_len - 1]);
> +	min_period = div64_u64((u64)NSEC_PER_SEC * (1 << pwm_resolution_arr[0]),
> +			       clk_rate_arr[clk_len - 1]);
>   	if (period <= min_period)
>   		return -EINVAL;
>   
>   	/* Limit period to largest possible value, to avoid overflows */
> -	max_period = (u64)NSEC_PER_SEC * max_res * LPG_MAX_PREDIV *
> -			div64_u64((1 << LPG_MAX_M), 1024);
> +	max_period = div64_u64((u64)NSEC_PER_SEC * max_res * LPG_MAX_PREDIV * (1 << LPG_MAX_M),
> +			       1024);
>   	if (period > max_period)
>   		period = max_period;
>   

Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8550-QRD