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| author | Thierry Reding <thierry.reding@gmail.com> | 2019-10-17 12:56:00 +0200 |
|---|---|---|
| committer | Thierry Reding <thierry.reding@gmail.com> | 2019-12-09 10:05:43 +0100 |
| commit | a3597d6c89d70ff0bcb1dd74dc0a88442fe79da6 (patch) | |
| tree | 302f0ee7904e2c5221b200675f50322be716535f /drivers/pwm/pwm-imx27.c | |
| parent | 1db37f9561b2b3f57d84b6253a9cd97f6289f8e1 (diff) | |
| download | lwn-a3597d6c89d70ff0bcb1dd74dc0a88442fe79da6.tar.gz lwn-a3597d6c89d70ff0bcb1dd74dc0a88442fe79da6.zip | |
pwm: imx27: Cache duty cycle register value
The hardware register containing the duty cycle value cannot be accessed
when the PWM is disabled. This causes the ->get_state() callback to read
back a duty cycle value of 0, which can confuse consumer drivers.
Tested-by: Michal Vokáč <michal.vokac@ysoft.com>
Tested-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Diffstat (limited to 'drivers/pwm/pwm-imx27.c')
| -rw-r--r-- | drivers/pwm/pwm-imx27.c | 31 |
1 files changed, 24 insertions, 7 deletions
diff --git a/drivers/pwm/pwm-imx27.c b/drivers/pwm/pwm-imx27.c index ae11d8577f18..4113d5cd4c62 100644 --- a/drivers/pwm/pwm-imx27.c +++ b/drivers/pwm/pwm-imx27.c @@ -85,6 +85,13 @@ struct pwm_imx27_chip { struct clk *clk_per; void __iomem *mmio_base; struct pwm_chip chip; + + /* + * The driver cannot read the current duty cycle from the hardware if + * the hardware is disabled. Cache the last programmed duty cycle + * value to return in that case. + */ + unsigned int duty_cycle; }; #define to_pwm_imx27_chip(chip) container_of(chip, struct pwm_imx27_chip, chip) @@ -155,14 +162,17 @@ static void pwm_imx27_get_state(struct pwm_chip *chip, tmp = NSEC_PER_SEC * (u64)(period + 2); state->period = DIV_ROUND_CLOSEST_ULL(tmp, pwm_clk); - /* PWMSAR can be read only if PWM is enabled */ - if (state->enabled) { + /* + * PWMSAR can be read only if PWM is enabled. If the PWM is disabled, + * use the cached value. + */ + if (state->enabled) val = readl(imx->mmio_base + MX3_PWMSAR); - tmp = NSEC_PER_SEC * (u64)(val); - state->duty_cycle = DIV_ROUND_CLOSEST_ULL(tmp, pwm_clk); - } else { - state->duty_cycle = 0; - } + else + val = imx->duty_cycle; + + tmp = NSEC_PER_SEC * (u64)(val); + state->duty_cycle = DIV_ROUND_CLOSEST_ULL(tmp, pwm_clk); if (!state->enabled) pwm_imx27_clk_disable_unprepare(chip); @@ -261,6 +271,13 @@ static int pwm_imx27_apply(struct pwm_chip *chip, struct pwm_device *pwm, writel(duty_cycles, imx->mmio_base + MX3_PWMSAR); writel(period_cycles, imx->mmio_base + MX3_PWMPR); + /* + * Store the duty cycle for future reference in cases where + * the MX3_PWMSAR register can't be read (i.e. when the PWM + * is disabled). + */ + imx->duty_cycle = duty_cycles; + cr = MX3_PWMCR_PRESCALER_SET(prescale) | MX3_PWMCR_STOPEN | MX3_PWMCR_DOZEN | MX3_PWMCR_WAITEN | FIELD_PREP(MX3_PWMCR_CLKSRC, MX3_PWMCR_CLKSRC_IPG_HIGH) | |