Hello,
On Wed, Jul 10, 2024 at 10:04:07AM +0800, Binbin Zhou wrote:
> diff --git a/drivers/pwm/pwm-loongson.c b/drivers/pwm/pwm-loongson.c
> new file mode 100644
> index 000000000000..17ab2a2f48ad
> --- /dev/null
> +++ b/drivers/pwm/pwm-loongson.c
> @@ -0,0 +1,285 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Loongson PWM driver
> + *
> + * Author: Juxin Gao <gaojuxin@xxxxxxxxxxx>
> + * Further cleanup and restructuring by:
> + * Binbin Zhou <zhoubinbin@xxxxxxxxxxx>
> + *
> + * Copyright (C) 2017-2024 Loongson Technology Corporation Limited.
> + *
> + * Limitations:
> + * - The buffer register value should be written before the CTRL register.
> + * - When disabled the output is driven to 0 independent of the configured
> + * polarity.
An info about possible glitches and if a period is completed on
reconfiguration or when the PWM is disabled would be great.
Also if there is a publically available manual, please add a link here.
> + */
> +
> [...]
> +static int pwm_loongson_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> + const struct pwm_state *state)
> +{
> + int ret;
> + u64 period, duty_cycle;
> + bool enabled = pwm->state.enabled;
> +
> + if (enabled && !state->enabled) {
> + pwm_loongson_disable(chip, pwm);
> + return 0;
> + }
You can also shortcut if !pwm->state.enabled. Something like:
if (!state->enabled) {
if (enabled)
pwm_loongson_disable(chip, pwm);
return 0;
}
> + if (state->polarity != pwm->state.polarity) {
> + ret = pwm_loongson_set_polarity(chip, pwm, state->polarity);
> + if (ret)
> + return ret;
> + }
Together with the shortcut above this is buggy. Consider:
pwm_apply_might_sleep(mypwm, &(struct pwm_state){
.period = A,
.duty_cycle = B,
.polarity = PWM_POLARITY_NORMAL,
.enabled = true});
pwm_apply_might_sleep(mypwm, &(struct pwm_state){
.period = A,
.duty_cycle = B,
.polarity = PWM_POLARITY_INVERSED,
.enabled = false});
pwm_apply_might_sleep(mypwm, &(struct pwm_state){
.period = A,
.duty_cycle = B,
.polarity = PWM_POLARITY_INVERSED,
.enabled = true});
After the 2nd call you left pwm_loongson_apply() early without writing
the inversed polarity to the register space. In the 3rd call you have
state->polarity == pwm->state.polarity and so skip configuring the
polarity again.
I suggest to just do pwm_loongson_set_polarity() unconditionally if
state->enabled = true.
> + period = min(state->period, NANOHZ_PER_HZ);
> + duty_cycle = min(state->duty_cycle, NANOHZ_PER_HZ);
> +
> + ret = pwm_loongson_config(chip, pwm, duty_cycle, period);
> + if (ret)
> + return ret;
> +
> + if (!enabled && state->enabled)
> + ret = pwm_loongson_enable(chip, pwm);
> +
> + return ret;
> +}
Best regards
Uwe
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