Re: [PATCH v3 RESEND 02/11] pwm: imx: remove ipg clock

From: Stefan Agner <stefan@agner.ch>
To: Lukasz Majewski <l.majewski@majess.pl>
Cc: Thierry Reding <thierry.reding@gmail.com>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	linux-pwm@vger.kernel.org,
	Bhuvanchandra DV <bhuvanchandra.dv@toradex.com>,
	linux-kernel@vger.kernel.org,
	Fabio Estevam <fabio.estevam@nxp.com>,
	Fabio Estevam <festevam@gmail.com>,
	Boris Brezillon <boris.brezillon@free-electrons.com>,
	Lothar Wassmann <LW@karo-electronics.de>,
	kernel@pengutronix.de, Philipp Zabel <p.zabel@pengutronix.de>
Subject: Re: [PATCH v3 RESEND 02/11] pwm: imx: remove ipg clock
Date: Thu, 29 Dec 2016 08:22:06 +0100	[thread overview]
Message-ID: <9c77756a3a4a88664d070f27291fba3f@agner.ch> (raw)
In-Reply-To: <20161228230116.4bf078ce@jawa>

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@pengutronix.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.

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, 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...

I can prepare a patch.

--
Stefan

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