Re: [PATCH 05/14] pwm: rockchip: Avoid glitches on already running PWMs

Brian Norris
2016-06-03T20:28:59Z

Hi,

Just noticed a few things:

On Fri, Jun 03, 2016 at 10:23:03AM +0200, Boris Brezillon wrote:
> The current logic will disable the PWM clk even if the PWM was left
> enabled by the bootloader (because it's controlling a critical device
> like a regulator for example).
> Keep the PWM clk enabled if the PWM is enabled to avoid any glitches.
>
> Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
> ---
> drivers/pwm/pwm-rockchip.c | 24 +++++++++++++++++++++++-
> 1 file changed, 23 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pwm/pwm-rockchip.c b/drivers/pwm/pwm-rockchip.c
> index dfacf7d..798a787 100644
> --- a/drivers/pwm/pwm-rockchip.c
> +++ b/drivers/pwm/pwm-rockchip.c
> @@ -299,6 +299,7 @@ static int rockchip_pwm_probe(struct platform_device *pdev)
> {
> const struct of_device_id *id;
> struct rockchip_pwm_chip *pc;
> + struct pwm_state state;
> struct resource *r;
> int ret;
>
> @@ -319,7 +320,7 @@ static int rockchip_pwm_probe(struct platform_device *pdev)
> if (IS_ERR(pc->clk))
> return PTR_ERR(pc->clk);
>
> - ret = clk_prepare(pc->clk);
> + ret = clk_prepare_enable(pc->clk);
> if (ret)
> return ret;
>
> @@ -342,12 +343,33 @@ static int rockchip_pwm_probe(struct platform_device *pdev)
> dev_err(&pdev->dev, "pwmchip_add() failed: %d\n", ret);
> }
>
> + /* Keep the PWM clk enabled if the PWM appears to be up and running. */
> + pwm_get_state(pc->chip.pwms, &state);
> + if (!state.enabled)

Why not just if (!pwm_is_enabled())?

> + clk_disable(pc->clk);
> +
> return ret;
> }
>
> static int rockchip_pwm_remove(struct platform_device *pdev)
> {
> struct rockchip_pwm_chip *pc = platform_get_drvdata(pdev);
> + struct pwm_state state;
> +
> + /*
> + * Disable the PWM clk before unpreparing it if the PWM device is still
> + * running. This should only happen when the last PWM user left it
> + * enabled, or when nobody requested a PWM that was previously enabled
> + * by the bootloader.
> + *
> + * FIXME: Maybe the core should disable all PWM devices in
> + * pwmchip_remove(). In this case we'd only have to call
> + * clk_unprepare() after pwmchip_remove().
> + *
> + */
> + pwm_get_state(pc->chip.pwms, &state);
> + if (state.enabled)

Same here.

With that:

Reviewed-by: Brian Norris <briannorris@chromium.org>

And it tests out fine:

Tested-by: Brian Norris <briannorris@chromium.org>

> + clk_disable(pc->clk);
>
> clk_unprepare(pc->clk);
>
> --
> 2.7.4
>