Re: [PATCH v3 02/11] pwm: imx: remove ipg clock

Stefan Agner
2016-11-22T21:10:34Z

On 2016-11-01 00:10, Lukasz Majewski wrote:
> From: Sascha Hauer <s.hauer@pengutronix.de>
>
> The use of the ipg clock was introduced with commit 7b27c160c681
> ("pwm: i.MX: fix clock lookup").
> In the commit message it was claimed that the ipg clock is enabled for
> register accesses. This is true for the ->config() callback, but not
> for the ->set_enable() callback. Given that the ipg clock is not
> consistently enabled for all register accesses we can assume that either
> it is not required at all or that the current code does not work.
> Remove the ipg clock code for now so that it's no longer in the way of
> refactoring the driver.
>
> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> Cc: Philipp Zabel <p.zabel@pengutronix.de>

I have to NACK here, sorry guys.

Just tested this on a i.MX 7, the kernel freezes in imx_pwm_config, I
guess that is where the code accesses a register first.

The i.MX 7 DT (imx7s.dtsi) specifies the same clock for ipg and per, but
it seems that this clock is crucial for register access on i.MX 7:

clocks = <&clks IMX7D_PWM1_ROOT_CLK>,
<&clks IMX7D_PWM1_ROOT_CLK>;
clock-names = "ipg", "per";

So since the "per" clock is the same in the i.MX 7 case, imx_pwm_enable
worked...

I agree that the old code is a bit weird, especially that we get the
clock in imx_pwm_enable. It seems that all device trees specify a "ipg"
clock, so I guess we can get the clock at probe time for all variants of
this IP and just enable it on peripheral access...

--
Stefan

> ---
> [commit message text refactored by Lukasz Majewski <l.majewski@majess.pl>]
> ---
> Changes for v3:
> - New patch
> ---
> drivers/pwm/pwm-imx.c | 19 +------------------
> 1 file changed, 1 insertion(+), 18 deletions(-)
>
> diff --git a/drivers/pwm/pwm-imx.c b/drivers/pwm/pwm-imx.c
> index d600fd5..70609ef2 100644
> --- a/drivers/pwm/pwm-imx.c
> +++ b/drivers/pwm/pwm-imx.c
> @@ -49,7 +49,6 @@
>
> struct imx_chip {
> struct clk *clk_per;
> - struct clk *clk_ipg;
>
> void __iomem *mmio_base;
>
> @@ -204,17 +203,8 @@ static int imx_pwm_config(struct pwm_chip *chip,
> struct pwm_device *pwm, int duty_ns, int period_ns)
> {
> struct imx_chip *imx = to_imx_chip(chip);
> - int ret;
> -
> - ret = clk_prepare_enable(imx->clk_ipg);
> - if (ret)
> - return ret;
>
> - ret = imx->config(chip, pwm, duty_ns, period_ns);
> -
> - clk_disable_unprepare(imx->clk_ipg);
> -
> - return ret;
> + return imx->config(chip, pwm, duty_ns, period_ns);
> }
>
> static int imx_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
> @@ -293,13 +283,6 @@ static int imx_pwm_probe(struct platform_device *pdev)
> return PTR_ERR(imx->clk_per);
> }
>
> - imx->clk_ipg = devm_clk_get(&pdev->dev, "ipg");
> - if (IS_ERR(imx->clk_ipg)) {
> - dev_err(&pdev->dev, "getting ipg clock failed with %ld\n",
> - PTR_ERR(imx->clk_ipg));
> - return PTR_ERR(imx->clk_ipg);
> - }
> -
> imx->chip.ops = &imx_pwm_ops;
> imx->chip.dev = &pdev->dev;
> imx->chip.base = -1;