Hello, On Wed, Jan 11, 2023 at 08:02:50AM +0100, Uwe Kleine-König wrote: > On Wed, Jan 11, 2023 at 12:15:29AM +0000, Conor Dooley wrote: > > On Tue, Jan 10, 2023 at 11:48:05PM +0100, Uwe Kleine-König wrote: > > > On Wed, Dec 21, 2022 at 11:29:12AM +0000, Conor Dooley wrote: > > > > From: Conor Dooley > > > > > > + delay_us = DIV_ROUND_UP_ULL(remaining_ns, NSEC_PER_USEC); > > > > + if ((delay_us / 1000) > MAX_UDELAY_MS) > > > > + msleep(delay_us / 1000 + 1); > > > > > > Is this better than > > > > > > msleep(DIV_ROUND_UP(delay_us, 1000); > > > > > > ? Also I wonder about your usage of MAX_UDELAY_MS. This is about > > > > I probably started hacking on the example you gave and didn't notice > > the U. What I have here is ~what you suggested last time. > > A series with (up to now) 13 revisions and long delays between the > review rounds (which are mostly attributed to my time schedule) is > difficult to handle on both sides. Some repetition isn't easy to prevent > in such a case. Sorry for that. > > > > udelay() but you're using usleep_range()? > > > > > > > + else > > > > + usleep_range(delay_us, delay_us * 2); > > > > > > I wonder if there isn't a function that implements something like > > > > > > wait_until(mchp_core_pwm->update_timestamp); > > > > > > which would be a bit nicer than doing this by hand. Maybe fsleep()? > > > > That'd be fsleep(delay_us), but does at least clean up some of the > > messing. > > > > > > +static void mchp_core_pwm_apply_duty(struct pwm_chip *chip, struct pwm_device *pwm, > > > > + const struct pwm_state *state, u64 duty_steps, > > > > + u8 period_steps) > > > > +{ > > > > + struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip); > > > > + u8 posedge, negedge; > > > > + u8 period_steps_val = PREG_TO_VAL(period_steps); > > > > + > > > > + /* > > > > + * Setting posedge == negedge doesn't yield a constant output, > > > > + * so that's an unsuitable setting to model duty_steps = 0. > > > > + * In that case set the unwanted edge to a value that never > > > > + * triggers. > > > > + */ > > > > + if (state->polarity == PWM_POLARITY_INVERSED) { > > > > + negedge = !duty_steps ? period_steps_val : 0u; > > > > > > IMHO > > > > > > negedge = duty_steps ? 0 : period_steps_val; > > > > > > is a bit easier to parse. > > > > > > > + posedge = duty_steps; > > > > + } else { > > > > + posedge = !duty_steps ? period_steps_val : 0u; > > > > + negedge = duty_steps; > > > > + } > > > > > > The following code is equivalent: > > > > > > u8 first_edge = 0, second_edge = duty_steps; > > > > > > /* > > > * Setting posedge == negedge doesn't yield a constant output, > > > * so that's an unsuitable setting to model duty_steps = 0. > > > * In that case set the unwanted edge to a value that never > > > * triggers. > > > */ > > > if (duty_steps == 0) > > > first_edge = period_steps_val; > > > > > > if (state->polarity == PWM_POLARITY_INVERSED) { > > > negedge = first_edge; > > > posedge = second_edge; > > > } else { > > > posedge = first_edge; > > > negedge = second_edge; > > > } > > > > > > I'm not sure if it's easier to understand. What do you think? > > > > Despite having used them, I dislike ternary statements. > > My variant is a bit longer and uses more variables, but has less > repetition. I don't expect a relevant change on the generated code. I > slightly prefer my variant, but I let you choose which one you prefer. > > > > > + writel_relaxed(posedge, mchp_core_pwm->base + MCHPCOREPWM_POSEDGE(pwm->hwpwm)); > > > > + writel_relaxed(negedge, mchp_core_pwm->base + MCHPCOREPWM_NEGEDGE(pwm->hwpwm)); > > > > +} > > > > + > > > > +static void mchp_core_pwm_calc_period(const struct pwm_state *state, unsigned long clk_rate, > > > > + u16 *prescale, u8 *period_steps) > > > > +{ > > > > + u64 tmp; > > > > + > > > > + /* > > > > + * Calculate the period cycles and prescale values. > > > > + * The registers are each 8 bits wide & multiplied to compute the period > > > > + * using the formula: > > > > + * (clock_period) * (prescale + 1) * (period_steps + 1) > > > > + * so the maximum period that can be generated is 0x10000 times the > > > > + * period of the input clock. > > > > + * However, due to the design of the "hardware", it is not possible to > > > > + * attain a 100% duty cycle if the full range of period_steps is used. > > > > + * Therefore period_steps is restricted to 0xFE and the maximum multiple > > > > + * of the clock period attainable is 0xFF00. > > > > + */ > > > > + tmp = mul_u64_u64_div_u64(state->period, clk_rate, NSEC_PER_SEC); > > > > + > > > > + /* > > > > + * The hardware adds one to the register value, so decrement by one to > > > > + * account for the offset > > > > + */ > > > > + if (tmp >= MCHPCOREPWM_PERIOD_MAX) { > > > > + *prescale = MCHPCOREPWM_PRESCALE_MAX - 1; > > > > + *period_steps = MCHPCOREPWM_PERIOD_STEPS_MAX - 1; > > > > + > > > > + return; > > > > + } > > > > + > > > > + *prescale = div_u64(tmp, MCHPCOREPWM_PERIOD_STEPS_MAX); > > > > + /* PREG_TO_VAL() can produce a value larger than UINT8_MAX */ > > > > + *period_steps = div_u64(tmp, PREG_TO_VAL(*prescale)) - 1; > > > > > > This looks wrong, but I didn't think long about that. Did we discuss > > > this already and/or are you sure this is correct? > > > > We did discuss it previously AFAICT; > > https://lore.kernel.org/linux-pwm/896d73ac-05af-8673-8379-29011800be83@microchip.com/ > > > > [...] > > Unfortunately, I don't think I am seeing what you're seeing. > > Well, the calculation lands in the right ballpark for sure, but if my > intuition is right, it's not as exact as it could be. I need some time > with pencil and paper ... Just a small heads up: I thought a bit about that (without pencil and paper on my way to work today), and the optimal solution is non-trivial. In fact you have to pick parameters A and B such that for a given C (A + 1) * (B + 1) is maximal with 0 <= A < 0x100 0 <= B < 0xff (A + 1) * (B + 1) <= C A consistent non-optimal choice that is easier to calculate than a complete search would be nice. But I think we're not there yet. Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ |