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 09:32:45 +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 08:26:09 +0100
> Lukasz Majewski <lukma@...x.de> wrote:
> 
> > 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.
> 
> Well, when the changes are substantial it can be justified, but here
> the changes are trivial (2 lines changed), and I don't think it calls
> for an authorship change (unless Sascha doesn't want to take the
> responsibility for those 2 lines).
> 

I will correct this if v5 is required, otherwise I can re-send only
this single patch.

> > 
> > Is the rest of the series correct?
> 
> I'll have a look.

Ok.

> 
> > 
> > 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
> > 
> > --
> > 
> > DENX Software Engineering GmbH,      Managing Director: Wolfgang
> > Denk HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell,
> > Germany Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email:
> > wd@...x.de
> 




Best regards,

Lukasz Majewski

--

DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@...x.de