[PATCH v4 4/4] pwm: meson: make full use of common clock framework
Heiner Kallweit
hkallweit1 at gmail.com
Mon Apr 17 02:53:58 PDT 2023
On 17.04.2023 09:23, Neil Armstrong wrote:
> On 13/04/2023 07:54, Heiner Kallweit wrote:
>> Newer versions of the PWM block use a core clock with external mux,
>> divider, and gate. These components either don't exist any longer in
>> the PWM block, or they are bypassed.
>> To minimize needed changes for supporting the new version, the internal
>> divider and gate should be handled by CCF too.
>>
>> I didn't see a good way to split the patch, therefore it's somewhat
>> bigger. What it does:
>>
>> - The internal mux is handled by CCF already. Register also internal
>> divider and gate with CCF, so that we have one representation of the
>> input clock: [mux] parent of [divider] parent of [gate]
>> - Now that CCF selects an appropriate mux parent, we don't need the
>> DT-provided default parent any longer. Accordingly we can also omit
>> setting the mux parent directly in the driver.
>> - Instead of manually handling the pre-div divider value, let CCF
>> set the input clock. Targeted input clock frequency is
>> 0xffff * 1/period for best precision.
>> - For the "inverted pwm disabled" scenario target an input clock
>> frequency of 1GHz. This ensures that the remaining low pulses
>> have minimum length.
>>
>> I don't have hw with the old PWM block, therefore I couldn't test this
>> patch. With the not yet included extension for the new PWM block
>> (channel->clk coming directly from get_clk(external_clk)) I didn't
>> notice any problem. My system uses PWM for the CPU voltage regulator
>> and for the SDIO 32kHz clock.
>>
>> Note: The clock gate in the old PWM block is permanently disabled.
>> This seems to indicate that it's not used by the new PWM block.
>>
>> Tested-by: Martin Blumenstingl <martin.blumenstingl at googlemail.com>
>> Signed-off-by: Heiner Kallweit <hkallweit1 at gmail.com>
>> ---
>> Changes to RFT/RFC version:
>> - use parent_hws instead of parent_names for div/gate clock
>> - use devm_clk_hw_register where the struct clk * returned by
>> devm_clk_register isn't needed
>>
>> v2:
>> - add patch 1
>> - add patch 3
>> - switch to using clk_parent_data in all relevant places
>> v3:
>> - add flag CLK_IGNORE_UNUSED
>> v4:
>> - remove variable tmp in meson_pwm_get_state
>> - don't use deprecated function devm_clk_register
>> ---
>> drivers/pwm/pwm-meson.c | 142 +++++++++++++++++++++++-----------------
>> 1 file changed, 83 insertions(+), 59 deletions(-)
>>
>> diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c
>> index 40a8709ff..80ac71cbc 100644
>> --- a/drivers/pwm/pwm-meson.c
>> +++ b/drivers/pwm/pwm-meson.c
>> @@ -51,7 +51,7 @@
>> #define REG_MISC_AB 0x8
>> #define MISC_B_CLK_EN 23
>> #define MISC_A_CLK_EN 15
>> -#define MISC_CLK_DIV_MASK 0x7f
>> +#define MISC_CLK_DIV_WIDTH 7
>> #define MISC_B_CLK_DIV_SHIFT 16
>> #define MISC_A_CLK_DIV_SHIFT 8
>> #define MISC_B_CLK_SEL_SHIFT 6
>> @@ -87,12 +87,13 @@ static struct meson_pwm_channel_data {
>> };
>> struct meson_pwm_channel {
>> + unsigned long rate;
>> unsigned int hi;
>> unsigned int lo;
>> - u8 pre_div;
>> - struct clk *clk_parent;
>> struct clk_mux mux;
>> + struct clk_divider div;
>> + struct clk_gate gate;
>> struct clk *clk;
>> };
>> @@ -125,16 +126,6 @@ static int meson_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm)
>> struct device *dev = chip->dev;
>> int err;
>> - if (channel->clk_parent) {
>> - err = clk_set_parent(channel->clk, channel->clk_parent);
>> - if (err < 0) {
>> - dev_err(dev, "failed to set parent %s for %s: %d\n",
>> - __clk_get_name(channel->clk_parent),
>> - __clk_get_name(channel->clk), err);
>> - return err;
>> - }
>> - }
>> -
>> err = clk_prepare_enable(channel->clk);
>> if (err < 0) {
>> dev_err(dev, "failed to enable clock %s: %d\n",
>> @@ -157,8 +148,9 @@ static int meson_pwm_calc(struct meson_pwm *meson, struct pwm_device *pwm,
>> const struct pwm_state *state)
>> {
>> struct meson_pwm_channel *channel = &meson->channels[pwm->hwpwm];
>> - unsigned int duty, period, pre_div, cnt, duty_cnt;
>> + unsigned int duty, period, cnt, duty_cnt;
>> unsigned long fin_freq;
>> + u64 freq;
>> duty = state->duty_cycle;
>> period = state->period;
>> @@ -166,7 +158,11 @@ static int meson_pwm_calc(struct meson_pwm *meson, struct pwm_device *pwm,
>> if (state->polarity == PWM_POLARITY_INVERSED)
>> duty = period - duty;
>> - fin_freq = clk_get_rate(channel->clk);
>> + freq = div64_u64(NSEC_PER_SEC * (u64)0xffff, period);
>> + if (freq > ULONG_MAX)
>> + freq = ULONG_MAX;
>> +
>> + fin_freq = clk_round_rate(channel->clk, freq);
>> if (fin_freq == 0) {
>> dev_err(meson->chip.dev, "invalid source clock frequency\n");
>> return -EINVAL;
>> @@ -174,46 +170,35 @@ static int meson_pwm_calc(struct meson_pwm *meson, struct pwm_device *pwm,
>> dev_dbg(meson->chip.dev, "fin_freq: %lu Hz\n", fin_freq);
>> - pre_div = div64_u64(fin_freq * (u64)period, NSEC_PER_SEC * 0xffffLL);
>> - if (pre_div > MISC_CLK_DIV_MASK) {
>> - dev_err(meson->chip.dev, "unable to get period pre_div\n");
>> - return -EINVAL;
>> - }
>> -
>> - cnt = div64_u64(fin_freq * (u64)period, NSEC_PER_SEC * (pre_div + 1));
>> + cnt = div64_u64(fin_freq * (u64)period, NSEC_PER_SEC);
>> if (cnt > 0xffff) {
>> dev_err(meson->chip.dev, "unable to get period cnt\n");
>> return -EINVAL;
>> }
>> - dev_dbg(meson->chip.dev, "period=%u pre_div=%u cnt=%u\n", period,
>> - pre_div, cnt);
>> + dev_dbg(meson->chip.dev, "period=%u cnt=%u\n", period, cnt);
>> if (duty == period) {
>> - channel->pre_div = pre_div;
>> channel->hi = cnt;
>> channel->lo = 0;
>> } else if (duty == 0) {
>> - channel->pre_div = pre_div;
>> channel->hi = 0;
>> channel->lo = cnt;
>> } else {
>> - /* Then check is we can have the duty with the same pre_div */
>> - duty_cnt = div64_u64(fin_freq * (u64)duty,
>> - NSEC_PER_SEC * (pre_div + 1));
>> + duty_cnt = div64_u64(fin_freq * (u64)duty, NSEC_PER_SEC);
>> if (duty_cnt > 0xffff) {
>> dev_err(meson->chip.dev, "unable to get duty cycle\n");
>> return -EINVAL;
>> }
>> - dev_dbg(meson->chip.dev, "duty=%u pre_div=%u duty_cnt=%u\n",
>> - duty, pre_div, duty_cnt);
>> + dev_dbg(meson->chip.dev, "duty=%u duty_cnt=%u\n", duty, duty_cnt);
>> - channel->pre_div = pre_div;
>> channel->hi = duty_cnt;
>> channel->lo = cnt - duty_cnt;
>> }
>> + channel->rate = fin_freq;
>> +
>> return 0;
>> }
>> @@ -223,16 +208,15 @@ static void meson_pwm_enable(struct meson_pwm *meson, struct pwm_device *pwm)
>> struct meson_pwm_channel_data *channel_data;
>> unsigned long flags;
>> u32 value;
>> + int err;
>> channel_data = &meson_pwm_per_channel_data[pwm->hwpwm];
>> - spin_lock_irqsave(&meson->lock, flags);
>> + err = clk_set_rate(channel->clk, channel->rate);
>> + if (err)
>> + dev_err(meson->chip.dev, "setting clock rate failed\n");
>> - value = readl(meson->base + REG_MISC_AB);
>> - value &= ~(MISC_CLK_DIV_MASK << channel_data->clk_div_shift);
>> - value |= channel->pre_div << channel_data->clk_div_shift;
>> - value |= BIT(channel_data->clk_en_bit);
>> - writel(value, meson->base + REG_MISC_AB);
>> + spin_lock_irqsave(&meson->lock, flags);
>> value = FIELD_PREP(PWM_HIGH_MASK, channel->hi) |
>> FIELD_PREP(PWM_LOW_MASK, channel->lo);
>> @@ -271,16 +255,16 @@ static int meson_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>> /*
>> * This IP block revision doesn't have an "always high"
>> * setting which we can use for "inverted disabled".
>> - * Instead we achieve this using the same settings
>> - * that we use a pre_div of 0 (to get the shortest
>> - * possible duration for one "count") and
>> + * Instead we achieve this by setting an arbitrary,
>> + * very high frequency, resulting in the shortest
>> + * possible duration for one "count" and
>> * "period == duty_cycle". This results in a signal
>> * which is LOW for one "count", while being HIGH for
>> * the rest of the (so the signal is HIGH for slightly
>> * less than 100% of the period, but this is the best
>> * we can achieve).
>> */
>> - channel->pre_div = 0;
>> + channel->rate = 1000000000;
>> channel->hi = ~0;
>> channel->lo = 0;
>
> This looks like a really bad idea... please don't do that and instead introduce
> some pinctrl states where we set the PWM pin as GPIO mode high/low state like we
> did for SPI:
> https://lore.kernel.org/r/20221004-up-aml-fix-spi-v4-2-0342d8e10c49@baylibre.com
>
There's no behavior change in this patch set. So my understanding is that you'd
like to change the current behavior independent of the CCF-related changes.
For the updated PWM block (at least for S905X3, not sure with which family Amlogic
extended the PWM block) we have an integrated option to achieve constant low/high
output. It's just not implemented yet, it's something I may do as next step.
The extended PWM block added new bits pwm_A/B_constant_en that prevent the default
increment of the hi/lo period. By supporting these bits we can achieve value 0
for hi/lo.
IMO that's easier than adding pinctrl handling. The remaining question would be
whether it's worth it to add pinctrl handling just for the legacy version of the
PWM block.
More information about the linux-amlogic
mailing list