linux-kernel - Re: [PATCH RFC 2/3] watchdog: rzg2l

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Date: Fri, 21 Jun 2024 09:16:28 +0300
From: claudiu beznea <claudiu.beznea@...on.dev>
To: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc: ulf.hansson@...aro.org, wim@...ux-watchdog.org, linux@...ck-us.net,
 rafael@...nel.org, linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-watchdog@...r.kernel.org, geert+renesas@...der.be,
 linux-renesas-soc@...r.kernel.org,
 Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH RFC 2/3] watchdog: rzg2l_wdt: Keep the clocks prepared

Hi, Prabhakar,

On 20.06.2024 18:31, Lad, Prabhakar wrote:
> Hi Claudiu,
> 
> Thank you for the patch.
> 
> On Thu, Jun 20, 2024 at 9:29 AM Claudiu <claudiu.beznea@...on.dev> wrote:
>>
>> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>>
>> The watchdog restart handler is called with interrupts disabled. In
>> rzg2l_wdt_restart() we call clk_prepare_enable() to enable the watchdog
>> clocks. The prepare part of clk_prepare_enable() may sleep. Sleep in
>> atomic context should not happen. The clock drivers for all the
>> micro-architectures where the RZ/G2L watchdog driver is used are not
>> implementing struct clk_ops::prepare(). Even so, to be sure we are
>> not hitted by this at some point, keep the watchdog clocks prepared
>> and only enable them in restart handler. It is guaranteed that
>> clk_enable() can be called in atomic context.
>>
>> Reported-by: Ulf Hansson <ulf.hansson@...aro.org>
>> Closes: https://lore.kernel.org/all/CAPDyKFq1+cL1M9qGY0P58ETHUZHGymxQL0w92emUJPMe7a_GxA@mail.gmail.com
>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>> ---
>>  drivers/watchdog/rzg2l_wdt.c | 31 ++++++++++++++++++++++++++-----
>>  1 file changed, 26 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/watchdog/rzg2l_wdt.c b/drivers/watchdog/rzg2l_wdt.c
>> index 2a35f890a288..6e3d7512f38c 100644
>> --- a/drivers/watchdog/rzg2l_wdt.c
>> +++ b/drivers/watchdog/rzg2l_wdt.c
>> @@ -166,8 +166,8 @@ static int rzg2l_wdt_restart(struct watchdog_device *wdev,
>>         struct rzg2l_wdt_priv *priv = watchdog_get_drvdata(wdev);
>>         int ret;
>>
>> -       clk_prepare_enable(priv->pclk);
>> -       clk_prepare_enable(priv->osc_clk);
>> +       clk_enable(priv->pclk);
>> +       clk_enable(priv->osc_clk);
>>
> I think we need to add a check before enabling the clocks:
> 
> if (!watchdog_active(wdev)) {

Agree, this should be better.

>          clk_enable(priv->pclk);
>          clk_enable(priv->osc_clk);
> }
> 
>>         if (priv->devtype == WDT_RZG2L) {
>>                 ret = reset_control_deassert(priv->rstc);
>> @@ -226,11 +226,28 @@ static const struct watchdog_ops rzg2l_wdt_ops = {
>>         .restart = rzg2l_wdt_restart,
>>  };
>>
>> +static int rzg2l_clks_prepare(struct rzg2l_wdt_priv *priv)
>> +{
>> +       int ret;
>> +
>> +       ret = clk_prepare(priv->pclk);
>> +       if (ret)
>> +               return ret;
>> +
>> +       ret = clk_prepare(priv->osc_clk);
>> +       if (ret)
>> +               clk_unprepare(priv->pclk);
>> +
>> +       return ret;
>> +}
>> +
>>  static void rzg2l_wdt_pm_disable(void *data)
>>  {
>> -       struct watchdog_device *wdev = data;
>> +       struct rzg2l_wdt_priv *priv = data;
>>
>> -       pm_runtime_disable(wdev->parent);
>> +       pm_runtime_disable(priv->wdev.parent);
>> +       clk_unprepare(priv->osc_clk);
>> +       clk_unprepare(priv->pclk);
>>  }
>>
> All the above chunk can go away if we use devm_clk_get_prepared()
> while requesting the clocks in the probe.

Indeed, I missed devm_clk_get_prepared().

Thank you for your review,
Claudiu Beznea

> 
> Cheers,
> Prabhakar
> 
>>  static int rzg2l_wdt_probe(struct platform_device *pdev)
>> @@ -275,6 +292,10 @@ static int rzg2l_wdt_probe(struct platform_device *pdev)
>>
>>         priv->devtype = (uintptr_t)of_device_get_match_data(dev);
>>
>> +       ret = rzg2l_clks_prepare(priv);
>> +       if (ret)
>> +               return ret;
>> +
>>         pm_runtime_enable(&pdev->dev);
>>
>>         priv->wdev.info = &rzg2l_wdt_ident;
>> @@ -287,7 +308,7 @@ static int rzg2l_wdt_probe(struct platform_device *pdev)
>>
>>         watchdog_set_drvdata(&priv->wdev, priv);
>>         dev_set_drvdata(dev, priv);
>> -       ret = devm_add_action_or_reset(&pdev->dev, rzg2l_wdt_pm_disable, &priv->wdev);
>> +       ret = devm_add_action_or_reset(&pdev->dev, rzg2l_wdt_pm_disable, &priv);
>>         if (ret)
>>                 return ret;
>>
>> --
>> 2.39.2
>>
>>