Re: [PATCH v2 03/10] pwm: imx: Rewrite imx_pwm_*_v1 code to facilitate switch to atomic pwm operation

[Lukasz Majewski]

Hi Sascha,

> On Mon, Oct 31, 2016 at 06:59:04AM +0100, Sascha Hauer wrote:
> > On Thu, Oct 27, 2016 at 09:40:05AM +0200, Boris Brezillon wrote:
> > > On Thu, 27 Oct 2016 08:29:39 +0200
> > > Lukasz Majewski <l.majewski@xxxxxxxxx> wrote:
> > > 
> > > > The code has been rewritten to remove "generic" calls to
> > > > imx_pwm_{enable|disable|config}.
> > > > 
> > > > Such approach would facilitate switch to atomic PWM (a.k.a
> > > > ->apply()) implementation.
> > > > 
> > > > Suggested-by: Stefan Agner <stefan@xxxxxxxx>
> > > > Suggested-by: Boris Brezillon
> > > > <boris.brezillon@xxxxxxxxxxxxxxxxxx> Signed-off-by: Lukasz
> > > > Majewski <l.majewski@xxxxxxxxx> ---
> > > > Changes for v2:
> > > > - Add missing clock unprepare for clk_ipg
> > > > - Enable peripheral PWM clock (clk_per)
> > > > ---
> > > >  drivers/pwm/pwm-imx.c | 50
> > > > ++++++++++++++++++++++++++++++++++++++------------ 1 file
> > > > changed, 38 insertions(+), 12 deletions(-)
> > > > 
> > > > diff --git a/drivers/pwm/pwm-imx.c b/drivers/pwm/pwm-imx.c
> > > > index ea3ce79..822eb5a 100644
> > > > --- a/drivers/pwm/pwm-imx.c
> > > > +++ b/drivers/pwm/pwm-imx.c
> > > > @@ -65,8 +65,6 @@ struct imx_chip {
> > > >  static int imx_pwm_config_v1(struct pwm_chip *chip,
> > > >  		struct pwm_device *pwm, int duty_ns, int
> > > > period_ns) {
> > > > -	struct imx_chip *imx = to_imx_chip(chip);
> > > > -
> > > >  	/*
> > > >  	 * The PWM subsystem allows for exact frequencies.
> > > > However,
> > > >  	 * I cannot connect a scope on my device to the PWM
> > > > line and @@ -84,26 +82,56 @@ static int
> > > > imx_pwm_config_v1(struct pwm_chip *chip,
> > > >  	 * both the prescaler (/1 .. /128) and then by CLKSEL
> > > >  	 * (/2 .. /16).
> > > >  	 */
> > > > +	struct imx_chip *imx = to_imx_chip(chip);
> > > >  	u32 max = readl(imx->mmio_base + MX1_PWMP);
> > > >  	u32 p = max * duty_ns / period_ns;
> > > > +	int ret;
> > > > +
> > > > +	ret = clk_prepare_enable(imx->clk_ipg);
> > > > +	if (ret)
> > > > +		return ret;
> > > > +
> > > >  	writel(max - p, imx->mmio_base + MX1_PWMS);
> > > >  
> > > > +	clk_disable_unprepare(imx->clk_ipg);
> > > > +
> > > >  	return 0;
> > > >  }
> > > >  
> > > > -static void imx_pwm_set_enable_v1(struct pwm_chip *chip, bool
> > > > enable) +static int imx_pwm_enable_v1(struct pwm_chip *chip,
> > > > struct pwm_device *pwm) {
> > > >  	struct imx_chip *imx = to_imx_chip(chip);
> > > > +	int ret;
> > > >  	u32 val;
> > > >  
> > > > +	ret = clk_prepare_enable(imx->clk_ipg);
> > > > +	if (ret)
> > > > +		return ret;
> > > > +
> > > > +	ret = clk_prepare_enable(imx->clk_per);
> > > > +	if (ret)
> > > > +		return ret;
> > > > +
> > > >  	val = readl(imx->mmio_base + MX1_PWMC);
> > > > +	val |= MX1_PWMC_EN;
> > > > +	writel(val, imx->mmio_base + MX1_PWMC);
> > > >  
> > > > -	if (enable)
> > > > -		val |= MX1_PWMC_EN;
> > > > -	else
> > > > -		val &= ~MX1_PWMC_EN;
> > > > +	clk_disable_unprepare(imx->clk_ipg);
> > > > +
> > > > +	return 0;
> > > > +}
> > > > +
> > > > +static void imx_pwm_disable_v1(struct pwm_chip *chip, struct
> > > > pwm_device *pwm) +{
> > > > +	struct imx_chip *imx = to_imx_chip(chip);
> > > > +	u32 val;
> > > > +
> > > > +	val = readl(imx->mmio_base + MX1_PWMC);
> > > > +	val &= ~MX1_PWMC_EN;
> > > >  
> > > >  	writel(val, imx->mmio_base + MX1_PWMC);
> > > 
> > > Are you sure you don't need to enable the ipg clk when
> > > manipulating the PWMC register?
> > > If it's not needed here, then it's probably not needed in
> > > imx_pwm_enable_v1() either.
> > 
> > As said, even the commit 7b27c160c68 introducing the register clk
> > did not enable the clock consistently for all register accesses.
> > Maybe it's best to include the following patch so that we can find
> > a clear culprit and do not bury the ipg clock changes in larger
> > patches.
> > 
> > Sascha
> > 
> > -----------------------------8<-----------------------------------
> > 
> > From 30b77e83269a58c2cb5ce6de8be647e027030d34 Mon Sep 17 00:00:00
> > 2001 From: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
> > Date: Mon, 31 Oct 2016 06:45:33 +0100
> > Subject: [PATCH] pwm: imx: remove ipg clock
> > 
> > The use of the ipg clock was introduced with commit 7b27c160c6. 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.
> 
> For reference:
> 
> I verified on i.MX53 and i.MX25 that the ipg clock provided to the pwm
> driver is not needed when accessing registers.

In the v3 of the patch series (almost done) I can confirm that i.MX6q
works without ipg clock manipulation to access registers.

> I would have to verify
> that on i.MX27 aswell, but I do not have a board handy at the moment.
> 
> The current assumption as discussed by Philipp and me is that the ipg
> clk is only needed when the pwm output is driven by the ipg clk
> (MX3_PWMCR[16:17] = MX3_PWMCR_CLKSRC_IPG)

Interresting .... I must check if I'm able to test this on my (rather)
not accessible HW.

Best regards,
Åukasz Majewski

> 
> Sascha
>

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