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

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Date:   Thu, 5 Jan 2017 08:26:09 +0100
From:   Lukasz Majewski <lukma@...x.de>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Stefan Agner <stefan@...er.ch>, 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

Hi Boris,

> On Thu,  5 Jan 2017 00:36:45 +0100
> Lukasz Majewski <lukma@...x.de> wrote:
> 
> > From: Boris Brezillon <boris.brezillon@...e-electrons.com>
> 
> Can you keep Sascha as the author of this patch?

But the patch differs from the original one - and that change was sent
by you - so I assume that you made the modifications.

Apparently there are two authors and we only have one "Author"
field :-) so I took the patch as it was sent by you.

Is the rest of the series correct?

Best regards,
Łukasz Majewski

> 
> > 
> > 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
> > 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.
> > 
> > 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>
> > ---
> > 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;
> 




Best regards,

Lukasz Majewski

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