Re: [PATCH v4 02/11] pwm: imx: remove ipg clock and enable per clock when required

Stefan Agner
2017-01-10T17:28:41Z

On 2017-01-04 15:36, Lukasz Majewski wrote:
> From: Boris Brezillon <boris.brezillon@free-electrons.com>
>
> 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.
>
> In the other hand, the imx7 IP requires the peripheral clock to be

Nit:

s/In/On?

> enabled before accessing its registers. Since ->config() can be called
> when the PWM is disabled (in which case, the peripheral clock is also
> disabled), we need to surround the imx->config() with
> clk_prepare_enable(per_clk)/clk_disable_unprepare(per_clk) calls.
>
> Note that the imx7 IP was working fine so far because the ipg clock was
> actually pointing to the peripheral clock, which guaranteed peripheral
> clock activation even when ->config() was called when the PWM was
> disabled.

That is not entirely true, but almost, I would say:

"Note that the driver was working fine for the i.MX 7 IP so far because
the ipg and peripheral clock use the same hardware clock gate, which
guaranteed..."

>
> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
> Cc: Philipp Zabel <p.zabel@pengutronix.de>

Reviewed-by: Stefan Agner <stefan@agner.ch>

Tried on-top of 4.10-rc3, only this patch, still works.

Tested-by: Stefan Agner <stefan@agner.ch>

--
Stefan

> ---
> Changes in v4:
> - Enable per clk before calling imx->config()
>
> Changes in v3:
> - New patch
> ---
> drivers/pwm/pwm-imx.c | 12 ++----------
> 1 file changed, 2 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/pwm/pwm-imx.c b/drivers/pwm/pwm-imx.c
> index d600fd5..b1d1e50 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;
>
> @@ -206,13 +205,13 @@ static int imx_pwm_config(struct pwm_chip *chip,
> struct imx_chip *imx = to_imx_chip(chip);
> int ret;
>
> - ret = clk_prepare_enable(imx->clk_ipg);
> + ret = clk_prepare_enable(imx->clk_per);
> if (ret)
> return ret;
>
> ret = imx->config(chip, pwm, duty_ns, period_ns);
>
> - clk_disable_unprepare(imx->clk_ipg);
> + clk_disable_unprepare(imx->clk_per);
>
> return ret;
> }
> @@ -293,13 +292,6 @@ 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;