Hi Uwe, On Thu, Oct 28, 2021 at 01:15:35PM +0200, Uwe Kleine-König wrote: > On Thu, Oct 28, 2021 at 10:14:42AM +0100, Sean Young wrote: > > On Thu, Oct 28, 2021 at 08:45:13AM +0200, Uwe Kleine-König wrote: > > > The conversion is right (I think), > > > > We still have the problem that the pwm drivers calculate the period > > incorrectly by rounding down (except pwm-bcm2835). So the period is not > > as good as it could be in most cases, but this driver can't do anything > > about that. > > Yeah, some time ago I started coding a round_state function > (wip at > https://git.pengutronix.de/cgit/ukl/linux/commit/?h=pwm-wip&id=ae348eb6a55d6526f30ef4a49819197d9616391e) > but this was pushed down on my todo-list by more important stuff. That looks great, thank you for working on that! > If you want to experiment with that ... I will have a look. > > > note this could be optimized a bit > > > further: state.period only depends on carrier which rarely changes, so > > > the calculation could be done in pwm_ir_set_carrier(). Ditto for duty > > > which only depends on state.period and pwm_ir->duty_cycle. (This is for > > > a separate commit though.) > > > > I'm not sure what caching this is much of a win. The calculation is a few > > instructions, so you're not winning in the way of speed. On the flip side > > you use more memory since pwm_state has to be kmalloc() rather than existing > > I tested a bit with this patch on top of Maíra's: > > diff --git a/drivers/media/rc/pwm-ir-tx.c b/drivers/media/rc/pwm-ir-tx.c > index 105a9c24f1e3..7585c21775bc 100644 > --- a/drivers/media/rc/pwm-ir-tx.c > +++ b/drivers/media/rc/pwm-ir-tx.c > @@ -17,7 +17,7 @@ > > struct pwm_ir { > struct pwm_device *pwm; > - unsigned int carrier; > + struct pwm_state state; > unsigned int duty_cycle; > }; > > @@ -32,6 +32,7 @@ static int pwm_ir_set_duty_cycle(struct rc_dev *dev, u32 duty_cycle) > struct pwm_ir *pwm_ir = dev->priv; > > pwm_ir->duty_cycle = duty_cycle; > + pwm_set_relative_duty_cycle(&pwm_ir->state, pwm_ir->duty_cycle, 100); > > return 0; > } > @@ -43,7 +44,8 @@ static int pwm_ir_set_carrier(struct rc_dev *dev, u32 carrier) > if (!carrier) > return -EINVAL; > > - pwm_ir->carrier = carrier; > + pwm_ir->state.period = DIV_ROUND_CLOSEST(NSEC_PER_SEC, carrier); > + pwm_set_relative_duty_cycle(&pwm_ir->state, pwm_ir->duty_cycle, 100); > > return 0; > } > @@ -53,21 +55,15 @@ static int pwm_ir_tx(struct rc_dev *dev, unsigned int *txbuf, > { > struct pwm_ir *pwm_ir = dev->priv; > struct pwm_device *pwm = pwm_ir->pwm; > - struct pwm_state state; > int i; > ktime_t edge; > long delta; > > - pwm_init_state(pwm, &state); > - > - state.period = DIV_ROUND_CLOSEST(NSEC_PER_SEC, pwm_ir->carrier); > - pwm_set_relative_duty_cycle(&state, pwm_ir->duty_cycle, 100); > - > edge = ktime_get(); > > for (i = 0; i < count; i++) { > - state.enabled = !(i % 2); > - pwm_apply_state(pwm, &state); > + pwm_ir->state.enabled = !(i % 2); > + pwm_apply_state(pwm, &pwm_ir->state); > > edge = ktime_add_us(edge, txbuf[i]); > delta = ktime_us_delta(edge, ktime_get()); > @@ -75,8 +71,8 @@ static int pwm_ir_tx(struct rc_dev *dev, unsigned int *txbuf, > usleep_range(delta, delta + 10); > } > > - state.enabled = false; > - pwm_apply_state(pwm, &state); > + pwm_ir->state.enabled = false; > + pwm_apply_state(pwm, &pwm_ir->state); > > return count; > } > @@ -95,8 +91,9 @@ static int pwm_ir_probe(struct platform_device *pdev) > if (IS_ERR(pwm_ir->pwm)) > return PTR_ERR(pwm_ir->pwm); > > - pwm_ir->carrier = 38000; > - pwm_ir->duty_cycle = 50; > + pwm_ir->state.duty_cycle = 50; > + pwm_init_state(pwm_ir->pwm, &pwm_ir->state); > + pwm_ir_set_carrier(rcdev, 38000); > > rcdev = devm_rc_allocate_device(&pdev->dev, RC_DRIVER_IR_RAW_TX); > if (!rcdev) > > bloat-o-meter reports (for an arm allmodconfig build) > > add/remove: 0/0 grow/shrink: 3/1 up/down: 644/-396 (248) > Function old new delta > pwm_ir_probe 372 676 +304 > pwm_ir_set_carrier 108 292 +184 > pwm_ir_set_duty_cycle 68 224 +156 > pwm_ir_tx 908 512 -396 > Total: Before=2302, After=2550, chg +10.77% So 248 bytes more after your changes. > struct pwm_ir increases from 12 bytes to 40 bytes. > > The stack space required by pwm_ir_tx decreases from 60 to 36 > > I don't know exactly how kmalloc works internally. Maybe allocating a > structure of size 40 bytes doesn't need more memory than a structure of > size 12? > > I didn't check how runtimes change, but the size decrease of pwm_ir_tx() > is nice and might save a bit of runtime. I'm not following, how is this decreasing runtime? > Probably it depends on your focus if this change is good for you or not. Decreasing size is of course a good thing. > > just on the stack, and both ioctl handlers and the probe function need to > > recalculate the period/duty cycle, so there is a slight increase in code size. > > > > This change does not improve anything measurably and only increases code > > complexity. > > You did measure? Thanks for prototyping this. Sean
