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

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

[Bjorn Andersson]

The introduction of high resolution PWM support moved the parenthesis of
the divisions in the calculation of min and max period. The result in
both divisions is in most cases 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")
Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>
---

This fixes the regression in v6.4-rc1.

 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] leds: qcom-lpg: Fix PWM period limits

[Steev Klimaszewski]

On Fri, May 12, 2023 at 11:55 AM Bjorn Andersson
<quic_bjorande@quicinc.com> wrote:
>
> The introduction of high resolution PWM support moved the parenthesis of
> the divisions in the calculation of min and max period. The result in
> both divisions is in most cases 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")
> Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>
> ---
>
> This fixes the regression in v6.4-rc1.
>
>  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
>
Thank you!
Without this fix, the display never activates on the Thinkpad X13s
Tested on the Lenovo Thinkpad X13s
Tested-by: Steev Klimaszewski <steev@kali.org>