Re: [PATCH 1/3] pwm: meson: Support constant and polarity bits

From: neil . armstrong
Date: Tue Oct 08 2024 - 04:13:17 EST

Hi,

On 07/10/2024 21:32, George Stark wrote:
Newer meson PWM IPs support constant and polarity bits. Support them to
correctly implement constant and inverted output levels.

Using constant bit allows to have truly stable low or high output level.
Since hi and low regs internally increment its values by 1 just writing
zero to any of them gives 1 clock count impulse. If constant bit is set
zero value in hi and low regs is not incremented.

Using polarity bit instead of swapping hi and low reg values allows to
correctly identify inversion in .get_state().

Signed-off-by: George Stark <gnstark@xxxxxxxxxxxxxxxxx>
---
drivers/pwm/pwm-meson.c | 75 +++++++++++++++++++++++++++++++++++++----
1 file changed, 69 insertions(+), 6 deletions(-)

diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c
index 98e6c1533312..5d51404bdce3 100644
--- a/drivers/pwm/pwm-meson.c
+++ b/drivers/pwm/pwm-meson.c
@@ -6,7 +6,7 @@
* PWM output is achieved by calculating a clock that permits calculating
* two periods (low and high). The counter then has to be set to switch after
* N cycles for the first half period.
- * The hardware has no "polarity" setting. This driver reverses the period
+ * Partly the hardware has no "polarity" setting. This driver reverses the period
* cycles (the low length is inverted with the high length) for
* PWM_POLARITY_INVERSED. This means that .get_state cannot read the polarity
* from the hardware.
@@ -56,6 +56,10 @@
#define MISC_B_CLK_SEL_SHIFT 6
#define MISC_A_CLK_SEL_SHIFT 4
#define MISC_CLK_SEL_MASK 0x3
+#define MISC_B_CONSTANT_EN BIT(29)
+#define MISC_A_CONSTANT_EN BIT(28)
+#define MISC_B_INVERT_EN BIT(27)
+#define MISC_A_INVERT_EN BIT(26)
#define MISC_B_EN BIT(1)
#define MISC_A_EN BIT(0)

Nice, seems I completely missed those 2 features!


@@ -68,6 +72,8 @@ static struct meson_pwm_channel_data {
u8 clk_div_shift;
u8 clk_en_shift;
u32 pwm_en_mask;
+ u32 const_en_mask;
+ u32 inv_en_mask;
} meson_pwm_per_channel_data[MESON_NUM_PWMS] = {
{
.reg_offset = REG_PWM_A,
@@ -75,6 +81,8 @@ static struct meson_pwm_channel_data {
.clk_div_shift = MISC_A_CLK_DIV_SHIFT,
.clk_en_shift = MISC_A_CLK_EN_SHIFT,
.pwm_en_mask = MISC_A_EN,
+ .const_en_mask = MISC_A_CONSTANT_EN,
+ .inv_en_mask = MISC_A_INVERT_EN,
},
{
.reg_offset = REG_PWM_B,
@@ -82,6 +90,8 @@ static struct meson_pwm_channel_data {
.clk_div_shift = MISC_B_CLK_DIV_SHIFT,
.clk_en_shift = MISC_B_CLK_EN_SHIFT,
.pwm_en_mask = MISC_B_EN,
+ .const_en_mask = MISC_B_CONSTANT_EN,
+ .inv_en_mask = MISC_B_INVERT_EN,
}
};

@@ -99,6 +109,8 @@ struct meson_pwm_channel {
struct meson_pwm_data {
const char *const parent_names[MESON_NUM_MUX_PARENTS];
int (*channels_init)(struct pwm_chip *chip);
+ bool has_constant;
+ bool has_polarity;
};

struct meson_pwm {
@@ -160,7 +172,7 @@ static int meson_pwm_calc(struct pwm_chip *chip, struct pwm_device *pwm,
* Fixing this needs some care however as some machines might rely on
* this.
*/
- if (state->polarity == PWM_POLARITY_INVERSED)
+ if (state->polarity == PWM_POLARITY_INVERSED && !meson->data->has_polarity)
duty = period - duty;

freq = div64_u64(NSEC_PER_SEC * 0xffffULL, period);
@@ -204,6 +216,46 @@ static int meson_pwm_calc(struct pwm_chip *chip, struct pwm_device *pwm,
return 0;
}

+static void meson_pwm_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm,
+ bool inverted)
+{
+ struct meson_pwm *meson = to_meson_pwm(chip);
+ const struct meson_pwm_channel_data *channel_data;
+ unsigned long flags;
+ u32 value;
+
+ channel_data = &meson_pwm_per_channel_data[pwm->hwpwm];
+
+ spin_lock_irqsave(&meson->lock, flags);
+ value = readl(meson->base + REG_MISC_AB);
+ if (inverted)
+ value |= channel_data->inv_en_mask;
+ else
+ value &= ~channel_data->inv_en_mask;
+ writel(value, meson->base + REG_MISC_AB);
+ spin_unlock_irqrestore(&meson->lock, flags);
+}
+
+static void meson_pwm_set_constant(struct pwm_chip *chip, struct pwm_device *pwm,
+ bool enable)
+{
+ struct meson_pwm *meson = to_meson_pwm(chip);
+ const struct meson_pwm_channel_data *channel_data;
+ unsigned long flags;
+ u32 value;
+
+ channel_data = &meson_pwm_per_channel_data[pwm->hwpwm];
+
+ spin_lock_irqsave(&meson->lock, flags);
+ value = readl(meson->base + REG_MISC_AB);
+ if (enable)
+ value |= channel_data->const_en_mask;
+ else
+ value &= ~channel_data->const_en_mask;
+ writel(value, meson->base + REG_MISC_AB);
+ spin_unlock_irqrestore(&meson->lock, flags);
+}

Those functions looks quite complicated, why can't they be part of
meson_pwm_enable/disable where we already write REG_MISC_AB ?

+
static void meson_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
{
struct meson_pwm *meson = to_meson_pwm(chip);
@@ -255,9 +307,9 @@ static int meson_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
int err = 0;

if (!state->enabled) {
- if (state->polarity == PWM_POLARITY_INVERSED) {
+ if (state->polarity == PWM_POLARITY_INVERSED && !meson->data->has_polarity) {
/*
- * This IP block revision doesn't have an "always high"
+ * Some of IP block revisions don't have an "always high"
* setting which we can use for "inverted disabled".
* Instead we achieve this by setting mux parent with
* highest rate and minimum divider value, resulting
@@ -284,6 +336,14 @@ static int meson_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
meson_pwm_enable(chip, pwm);
}

+ if (meson->data->has_constant)
+ meson_pwm_set_constant(chip, pwm,
+ state->duty_cycle == state->period ||
+ !state->duty_cycle);
+ if (meson->data->has_polarity)
+ meson_pwm_set_polarity(chip, pwm,
+ !(state->polarity == PWM_POLARITY_NORMAL));
+
return 0;
}

@@ -318,6 +378,11 @@ static int meson_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
value = readl(meson->base + REG_MISC_AB);
state->enabled = value & channel_data->pwm_en_mask;

+ if (meson->data->has_polarity && (value & channel_data->inv_en_mask))
+ state->polarity = PWM_POLARITY_INVERSED;
+ else
+ state->polarity = PWM_POLARITY_NORMAL;
+
value = readl(meson->base + channel_data->reg_offset);
channel->lo = FIELD_GET(PWM_LOW_MASK, value);
channel->hi = FIELD_GET(PWM_HIGH_MASK, value);
@@ -325,8 +390,6 @@ static int meson_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
state->period = meson_pwm_cnt_to_ns(chip, pwm, channel->lo + channel->hi);
state->duty_cycle = meson_pwm_cnt_to_ns(chip, pwm, channel->hi);

- state->polarity = PWM_POLARITY_NORMAL;
-
return 0;
}

--
2.25.1