Re: [PATCH v4 2/2] watchdog: Add watchdog driver for Sunplus SP7021

[Guenter Roeck]

On 12/30/21 6:50 PM, xt.hu[胡先韬] wrote:
> Hi Chrustophe,
>
> 	Thanks for your respond.
>
> Best Regards,
> Xiantao
> > -----Original Message-----
> > From: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
> > To: Xiantao Hu <xt.hu@xxxxxxxxxxx>,
> > 	wim@xxxxxxxxxxxxxxxxxx, p.zabel@xxxxxxxxxxxxxx,
> > 	linux-kernel@xxxxxxxxxxxxxxx, linux-watchdog@xxxxxxxxxxxxxxx,
> > 	linux@xxxxxxxxxxxx, robh+dt@xxxxxxxxxx,
> > 	devicetree@xxxxxxxxxxxxxxx
> > Cc: wells.lu@xxxxxxxxxxx, qinjian@xxxxxxxxxxx
> > Subject: Re: [PATCH v4 2/2] watchdog: Add watchdog driver for Sunplus SP7021
> > Date: Wed, 29 Dec 2021 10:39:08 +0100	[thread overview]
> > Message-ID: <0b102fa0-cbfc-a97e-8e7f-cce8146450bc@xxxxxxxxxx> (raw)
> > In-Reply-To: <20211229054308.63168-3-xt.hu@xxxxxxxxxxx>
> >
> > ...
> >
> > > +static int sp_wdt_probe(struct platform_device *pdev)
> > > +{
> > > +	struct device *dev = &pdev->dev;
> > > +	struct sp_wdt_priv *priv;
> > > +	int err;
> > > +
> > > +	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> > > +	if (!priv)
> > > +		return -ENOMEM;
> > > +
> > > +	priv->clk = devm_clk_get(dev, NULL);
> > > +	if (IS_ERR(priv->clk)) {
> > > +		dev_err(dev, "Can't find clock source\n");
> > > +		return PTR_ERR(priv->clk);
> > > +	}
> > > +
> > > +	err = clk_prepare_enable(priv->clk);
> > > +	if (err) {
> > > +		dev_err(dev, "Clock can't be enabled correctly\n");
> > > +		return err;
> > > +	}
> > > +
> > > +	/* The timer and watchdog shared the STC reset */
> > > +	priv->rstc = devm_reset_control_get_shared(dev, NULL);
> > > +	if (!IS_ERR(priv->rstc))
> > > +		reset_control_deassert(priv->rstc);
> > > +
> > > +	err = devm_add_action_or_reset(dev, sp_reset_control_assert,
> > > +				       priv->rstc);
> > > +	if (err)
> > > +		return err;
> > This looks odd.
> > We could undo something that was not done. (if IS_ERR(priv->rstc))
> > This is also not really consistent with what is done in suspedn/resume.
> > In these functions, we don't check for IS_ERR(priv->rstc).
>
> Here I refer to mt7621_wdt.c. I'm sure I need deassert reset to reset
> watchdog register value when driver probe. accordingly I assert reset
> in devm_add_action_or_reset() to ensure that the registers of watchdog
> can't be operated after module remove.

You are missing the point here. This is called even after
devm_reset_control_get_shared() failed, and it is called even though
the reset was not yet deasserted. The above code should be called after
(and only after) deasserting the reset.

> > > +
> > > +	err = devm_add_action_or_reset(dev, sp_clk_disable_unprepare,
> > > +				       priv->clk);
> > > +	if (err)
> > > +		return err;
> > Shouldn't this be just after clk_prepare_enable()?
>
> I tested the order of execution of the added functions which is similar to
> push and pop. First in, last out. I think I should disable clock last.
Correct. That is why you have to call devm_add_action_or_reset on disable_unprepare
first, because on driver removal the devm_ cleanup will be called in reverse order.

Guenter