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Date: Thu, 27 Feb 2014 05:10:10 +0000
From: "Li.Xiubo@...escale.com" <Li.Xiubo@...escale.com>
To: Thierry Reding <thierry.reding@...il.com>
CC: "linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Huan Wang <Huan.Wang@...escale.com>,
Jingchang Lu <jingchang.lu@...escale.com>
Subject: RE: [PATCHv9 Resend 1/4] pwm: Add Freescale FTM PWM driver support
Hi Thierry,
Thanks very much, I will fix them all.
:)
--
Best Regards,
Xiubo
> Sorry for taking so long to get back to you. Things have been quite busy
> lately. A few more comments below, but we're getting there.
>
> On Wed, Feb 19, 2014 at 04:38:54PM +0800, Xiubo Li wrote:
> [...]
> > diff --git a/drivers/pwm/pwm-fsl-ftm.c b/drivers/pwm/pwm-fsl-ftm.c
> [...]
> > +static unsigned long fsl_pwm_calculate_period(struct fsl_pwm_chip *fpc,
> > + unsigned long period_ns)
> > +{
> > + struct clk *cnt_clk[3];
> > + enum fsl_pwm_clk m0, m1;
> > + unsigned long fix_rate, ext_rate, cycles;
> > +
> > + fpc->counter_clk = fpc->sys_clk;
> > + cycles = fsl_pwm_calculate_period_cycles(fpc, period_ns,
> > + FSL_PWM_CLK_SYS);
> > + if (cycles)
> > + return cycles;
> > +
> > + cnt_clk[FSL_PWM_CLK_FIX] = devm_clk_get(fpc->chip.dev, "ftm_fix");
> > + if (IS_ERR(cnt_clk[FSL_PWM_CLK_FIX]))
> > + return PTR_ERR(cnt_clk[FSL_PWM_CLK_FIX]);
> > +
> > + cnt_clk[FSL_PWM_CLK_EXT] = devm_clk_get(fpc->chip.dev, "ftm_ext");
> > + if (IS_ERR(cnt_clk[FSL_PWM_CLK_EXT]))
> > + return PTR_ERR(cnt_clk[FSL_PWM_CLK_EXT]);
> > +
> > + fpc->counter_clk_en = devm_clk_get(fpc->chip.dev, "ftm_cnt_clk_en");
> > + if (IS_ERR(fpc->counter_clk_en))
> > + return PTR_ERR(fpc->counter_clk_en);
>
> You shouldn't do this. You're obtaining a reference to each of these
> clocks whenever pwm_config() is called. And devres will only clean those
> up after the driver is unbound. Can't you simply keep a reference to
> these within struct fsl_pwm_chip?
>
> > +static int fsl_counter_clock_enable(struct fsl_pwm_chip *fpc)
> > +{
> > + u32 val;
> > + int ret;
> > +
> > + if (fpc->counter_clk_enable++)
>
> This function is always called with the fpc->lock held, so you could
> make this much easier by incrementing the .counter_clk_enable field only
> at the very end of the function. That way...
>
> > + return 0;
> > +
> > + ret = clk_prepare_enable(fpc->counter_clk);
> > + if (ret) {
> > + fpc->counter_clk_enable--;
>
> ... this won't be necessary...
>
> > + return ret;
> > + }
> > +
> > + ret = clk_prepare_enable(fpc->counter_clk_en);
> > + if (ret) {
> > + fpc->counter_clk_enable--;
>
> ... and neither will this.
>
> > +static int fsl_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
> > +{
> > + struct fsl_pwm_chip *fpc = to_fsl_chip(chip);
> > + u32 val;
> > + int ret;
> > +
> > + val = readl(fpc->base + FTM_OUTMASK);
> > + val &= ~BIT(pwm->hwpwm);
> > + writel(val, fpc->base + FTM_OUTMASK);
> > +
> > + mutex_lock(&fpc->lock);
>
> I think you want to extend the lock to cover the FTM_OUTMASK register
> access as well because there could be a race between pwm_enable() and
> pwm_disable().
>
> > + ret = fsl_counter_clock_enable(fpc);
> > + mutex_unlock(&fpc->lock);
> > +
> > + return ret;
> > +}
>
> Can this function be moved somewhere else so fsl_counter_clock_enable()
> and fsl_counter_clock_disable() are grouped together?
>
> > +static void fsl_counter_clock_disable(struct fsl_pwm_chip *fpc)
> > +{
> > + u32 val;
> > +
> > + if (--fpc->counter_clk_enable)
> > + return;
>
> This is going to break. Consider the case where you call pwm_disable()
> on a PWM device and fpc->counter_clk_enable == 1. In that case, this
> will decrement counter_clk_enable to 0 and proceed with the remainder of
> this function.
>
> Now you call pwm_disable() again. The above will decrement again and
> cause fpc->counter_clk_enable to wrap around to UINT_MAX.
>
> So I think a more correct implementation would be:
>
> /*
> * already disabled, do nothing (perhaps output warning message
> * to catch unbalanced calls? )
> */
> if (fpc->counter_clk_enable == 0)
> return;
>
> /* there are still users, so can't disable yet */
> if (--fpc->counter_clk_enable > 0)
> return;
>
> /* no users left, disable clock */
>
> > +static void fsl_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
> > +{
> > + struct fsl_pwm_chip *fpc = to_fsl_chip(chip);
> > + u32 val;
> > +
> > + val = readl(fpc->base + FTM_OUTMASK);
> > + val |= BIT(pwm->hwpwm);
> > + writel(val, fpc->base + FTM_OUTMASK);
> > +
> > + mutex_lock(&fpc->lock);
>
> This lock should also include the access to FTM_OUTMASK above.
>
> > +static int fsl_pwm_probe(struct platform_device *pdev)
> > +{
> [...]
> > + fpc->sys_clk = devm_clk_get(&pdev->dev, "ftm_sys");
> > + if (IS_ERR(fpc->sys_clk)) {
> > + dev_err(&pdev->dev,
> > + "failed to get \"ftm_sys\" clock\n");
>
> The above easily fits on a single line, no need for the wrapping.
>
> > + return PTR_ERR(fpc->sys_clk);
> > + }
> > +
> > + ret = clk_prepare_enable(fpc->sys_clk);
> > + if (ret)
> > + return ret;
> > +
> > + writel(0x00, fpc->base + FTM_CNTIN);
> > + writel(0x00, fpc->base + FTM_OUTINIT);
> > + writel(0xFF, fpc->base + FTM_OUTMASK);
> > + clk_disable_unprepare(fpc->sys_clk);
>
> This looks out of place somehow, perhaps it should be moved off into a
> separate function? fsl_pwm_init() perhaps.
>
> Thierry
--
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