Re: [PATCH v3] backlight: lp855x: Switch to atomic PWM API

Em ter., 2 de nov. de 2021 às 05:39, Geert Uytterhoeven
[off-list ref] escreveu:

Hi Maíra,

On Sat, Oct 30, 2021 at 3:35 PM Maíra Canal [off-list ref] wrote:

quoted

Remove legacy PWM interface (pwm_config, pwm_enable, pwm_disable) and
replace it for the atomic PWM API.

Signed-off-by: Maíra Canal <redacted>

Thanks for your patch!

quoted

--- a/drivers/video/backlight/lp855x_bl.c
+++ b/drivers/video/backlight/lp855x_bl.c

@@ -233,9 +233,8 @@ static int lp855x_configure(struct lp855x *lp)

 static void lp855x_pwm_ctrl(struct lp855x *lp, int br, int max_br)
 {
-       unsigned int period = lp->pdata->period_ns;
-       unsigned int duty = br * period / max_br;
-       struct pwm_device *pwm;
+       struct pwm_device *pwm = NULL;
+       struct pwm_state state;

        /* request pwm device with the consumer name */
        if (!lp->pwm) {

@@ -245,18 +244,16 @@ static void lp855x_pwm_ctrl(struct lp855x *lp, int br, int max_br)

                lp->pwm = pwm;

-               /*
-                * FIXME: pwm_apply_args() should be removed when switching to
-                * the atomic PWM API.
-                */
-               pwm_apply_args(pwm);
+               pwm_init_state(lp->pwm, &state);
+               state.period = lp->pdata->period_ns;
        }

-       pwm_config(lp->pwm, duty, period);
-       if (duty)
-               pwm_enable(lp->pwm);
-       else
-               pwm_disable(lp->pwm);
+       pwm_get_state(lp->pwm, &state);
+
+       state.duty_cycle = br * state.period / max_br;

Above is a 64-by-32 division, which should not be open-coded, as
that will cause link failures on 32-bit platform (cfr. "undefined
reference to `__udivdi3'", as reported by the kernel test robot).
Please use div_u64() instead.

Hi Geert,

Thank you for the suggestion! I fixed this problem a bit differently
and submitted the v4. I made use of the PWM API and applied the
pwm_set_relative_duty_cycle function, which solved this division
problem.

quoted

+       state.enabled = state.duty_cycle;
+
+       pwm_apply_state(lp->pwm, &state);
 }

 static int lp855x_bl_update_status(struct backlight_device *bl)

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds