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

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Date:   Fri, 12 May 2023 17:05:19 -0500
From:   Steev Klimaszewski <steev@...i.org>
To:     Bjorn Andersson <quic_bjorande@...cinc.com>
Cc:     Pavel Machek <pavel@....cz>, Lee Jones <lee@...nel.org>,
        Anjelique Melendez <quic_amelende@...cinc.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Luca Weiss <luca@...tu.xyz>,
        linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] leds: qcom-lpg: Fix PWM period limits

On Fri, May 12, 2023 at 11:55 AM Bjorn Andersson
<quic_bjorande@...cinc.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@...cinc.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@...i.org>