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

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Date:   Tue, 10 Jan 2017 09:28:36 -0800
From:   Stefan Agner <stefan@...er.ch>
To:     Lukasz Majewski <lukma@...x.de>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        linux-pwm@...r.kernel.org,
        Bhuvanchandra DV <bhuvanchandra.dv@...adex.com>,
        linux-kernel@...r.kernel.org,
        Lothar Wassmann <LW@...o-electronics.de>,
        kernel@...gutronix.de, Fabio Estevam <fabio.estevam@....com>,
        Philipp Zabel <p.zabel@...gutronix.de>
Subject: Re: [PATCH v4 02/11] pwm: imx: remove ipg clock and enable per clock
 when required

On 2017-01-04 15:36, Lukasz Majewski wrote:
> From: Boris Brezillon <boris.brezillon@...e-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@...gutronix.de>
> Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
> Cc: Philipp Zabel <p.zabel@...gutronix.de>

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

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

Tested-by: Stefan Agner <stefan@...er.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;