Message-ID: <20161229110624.3544a7dd@jawa>
Date:   Thu, 29 Dec 2016 11:06:24 +0100
From:   Lukasz Majewski <l.majewski@...ess.pl>
To:     Stefan Agner <stefan@...er.ch>
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,
        Fabio Estevam <fabio.estevam@....com>,
        Fabio Estevam <festevam@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Lothar Wassmann <LW@...o-electronics.de>,
        kernel@...gutronix.de, Philipp Zabel <p.zabel@...gutronix.de>
Subject: Re: [PATCH v3 RESEND 02/11] pwm: imx: remove ipg clock

Hi Stefan,

> On 2016-12-28 23:01, Lukasz Majewski wrote:
> > Hi Stefan,
> > 
> >> Hi Stefan,
> >>
> >> > On 2016-12-26 23:55, Lukasz Majewski wrote:
> >> > > From: Sascha Hauer <s.hauer@...gutronix.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.
> >> >
> >> > Hi Lukasz,
> >> >
> >> > Has my concern addressed in any way with this resend?
> >> > https://lkml.org/lkml/2016/11/22/729
> >>
> >> Unfortunately not, since I don't have iMX7 for testing.
> >>
> >> >
> >> > Breaking hardware is usually not an option :-)
> >>
> >> Yes, I know, but
> >>
> >> Please look on the patch set from my perspective:
> >>
> >> I originally wanted to add polarity inversion to PWM. Then, there
> >> was the request from you and Boris to go with "atomicity" support,
> >> so I converted the driver to support it.
> >>
> >> This patch set has been resent on purpose at the end of merge
> >> window, so we do have some time to fix it if it would be accepted
> >> to -next tree (or any other PWM related one). Moreover, the burden
> >> for preparing patches would be smaller - since we all have agreed
> >> that "atomicity" is a more than welcome feature.
> >>
> >>
> >> >
> >> > I checked the i.MX 7 reference manual again, and in this case the
> >> > peripheral access clock is a clock line named "ipg_clk_s" (Table
> >> > 12-20), with a clock root "PWM1_CLK_ROOT" (Table 5-12). In i.MX 7
> >> > all clocks are behind a single gate, so in fact it does not
> >> > matter which clock we take. Given that others have peripheral
> >> > access behind the "pwm" gate, I guess we should take the "pwm"
> >> > gate...
> >>
> >>
> >> If possible please prepare a patch. It would be the best solution.
> > 
> > If I might ask - are you willing to prepare patch to fix iMX7 or
> > shall I roll back to the ipg code already present in main line ?
> 
> I doubt that just rolling back the existing code works for the new
> atomic change... I guess we have to really introduce a clk enable on
> each register access, also for the new atomic code.

Maybe this is a way to go.

> 
> Not sure if we should fold this change in a existing commit or create
> a new patch ontop of your changes. The latter is probably easier,

I would opt for creating (adding) changes on top of my changes.

> but
> creates a "window of brokenness" for i.MX 7 in git history. But then,
> I don't really mind since it currently works more or less by chance...

Hmm... it seems like Sascha patch (included to the patch series):

http://patchwork.ozlabs.org/patch/708847/

is a good starting point (at least we removed ipg clock) for fixing
things.

> 
> I can prepare a patch.

Thank you :-)

Best regards,
Łukasz Majewski

> 
> --
> Stefan
> 
> > 
> > 
> > Best regards,
> > Łukasz Majewski
> > 
> >>
> >> Thanks in advance,
> >> Łukasz Majewski
> >>
> >> >
> >> > --
> >> > Stefan
> >> >
> >> > >
> >> > > Signed-off-by: Sascha Hauer <s.hauer@...gutronix.de>
> >> > > Cc: Philipp Zabel <p.zabel@...gutronix.de>
> >> > > ---
> >> > > [commit message text refactored by Lukasz Majewski
> >> > > <l.majewski@...ess.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;
> >>


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