lkml.org 
[lkml]   [2023]   [Feb]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH v2 2/2] pwm: sifive: change the PWM controlled LED algorithm
    Hi Uwe,

    Thanks for your reply.

    Uwe Kleine-König <u.kleine-koenig@pengutronix.de> 於 2023年1月30日 週一 下午6:17寫道:
    >
    > On Mon, Jan 30, 2023 at 05:32:29PM +0800, Nylon Chen wrote:
    > > The `frac` variable represents the pulse inactive time, and the result of
    > > this algorithm is the pulse active time. Therefore, we must reverse the
    > > result.
    > >
    > > The reference is SiFive FU740-C000 Manual[0].
    > >
    > > [0]: https://sifive.cdn.prismic.io/sifive/1a82e600-1f93-4f41-b2d8-86ed8b16acba_fu740-c000-manual-v1p6.pdf
    > >
    > > Signed-off-by: Nylon Chen <nylon.chen@sifive.com>
    > > ---
    > > drivers/pwm/pwm-sifive.c | 1 +
    > > 1 file changed, 1 insertion(+)
    > >
    > > diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c
    > > index 62b6acc6373d..a5eda165d071 100644
    > > --- a/drivers/pwm/pwm-sifive.c
    > > +++ b/drivers/pwm/pwm-sifive.c
    > > @@ -158,6 +158,7 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
    > > frac = DIV64_U64_ROUND_CLOSEST(num, state->period);
    > > /* The hardware cannot generate a 100% duty cycle */
    > > frac = min(frac, (1U << PWM_SIFIVE_CMPWIDTH) - 1);
    > > + frac = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - frac;
    >
    > The same problem exists in pwm_sifive_get_state(), doesn't it?
    >
    > As fixing this is an interruptive change anyhow, this is the opportunity
    > to align the driver to the rules tested by PWM_DEBUG.
    >
    > The problems I see in the driver (only checked quickly, so I might be
    > wrong):
    >
    > - state->period != ddata->approx_period isn't necessarily a problem. If
    > state->period > ddata->real_period that's fine and the driver should
    > continue
    >
    > - frac = DIV64_U64_ROUND_CLOSEST(num, state->period);
    > is wrong for two reasons:
    > it should round down and use the real period.
    >
    I need a little time to clarify your assumptions. If possible, I will
    make similar changes.

    e.g.
    rounddown(num, state->period);
    if (state->period < ddata->approx_period)
    ...

    thanks a lot.






    > Best regards
    > Uwe
    >
    > --
    > Pengutronix e.K. | Uwe Kleine-König |
    > Industrial Linux Solutions | https://www.pengutronix.de/ |

    \
     
     \ /
      Last update: 2023-03-27 00:04    [W:6.383 / U:0.020 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site