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SubjectRe: [PATCH v4 2/2] watchdog: Add watchdog driver for Sunplus SP7021
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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@wanadoo.fr>
>> To: Xiantao Hu <xt.hu@cqplus1.com>,
>> wim@linux-watchdog.org, p.zabel@pengutronix.de,
>> linux-kernel@vger.kernel.org, linux-watchdog@vger.kernel.org,
>> linux@roeck-us.net, robh+dt@kernel.org,
>> devicetree@vger.kernel.org
>> Cc: wells.lu@sunplus.com, qinjian@cqplus1.com
>> 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@wanadoo.fr> (raw)
>> In-Reply-To: <20211229054308.63168-3-xt.hu@cqplus1.com>
>>
>> ...
>>
>>> +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

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