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

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

Posted by Bjorn Andersson 2 years, 8 months ago

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

Posted by Neil Armstrong 2 years, 8 months ago

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

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

Posted by Johan Hovold 2 years, 8 months ago

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

Posted by Lee Jones 2 years, 8 months ago

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

Posted by Johan Hovold 2 years, 8 months ago

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

Posted by Lee Jones 2 years, 8 months ago

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]