linux-kernel - Re: [PATCH v3 3/7] watchdog: npcm: Enable clock if provided

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Date:   Mon, 9 May 2022 19:31:31 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Jonathan Neuschäfer <j.neuschaefer@....net>,
        linux-clk@...r.kernel.org, openbmc@...ts.ozlabs.org
Cc:     linux-kernel@...r.kernel.org, linux-watchdog@...r.kernel.org,
        devicetree@...r.kernel.org,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Avi Fishman <avifishman70@...il.com>,
        Tomer Maimon <tmaimon77@...il.com>,
        Tali Perry <tali.perry1@...il.com>,
        Patrick Venture <venture@...gle.com>,
        Nancy Yuen <yuenn@...gle.com>,
        Benjamin Fair <benjaminfair@...gle.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>
Subject: Re: [PATCH v3 3/7] watchdog: npcm: Enable clock if provided

On 5/8/22 12:43, Jonathan Neuschäfer wrote:
> On the Nuvoton WPCM450 SoC, with its upcoming clock driver, peripheral
> clocks are individually gated and ungated. Therefore, the watchdog
> driver must be able to ungate the watchdog clock.
> 
> Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@....net>
> ---
> 
> v3:
> - Add enable/disable calls to npcm_wdt_restart handler
> - Not applied due to the above change:  Acked-by: Guenter Roeck <linux@...ck-us.net>
> 
> v2:
> - https://lore.kernel.org/lkml/20220429172030.398011-4-j.neuschaefer@gmx.net/
> - Add clk_disable_unprepare call, suggested by Guenter Roeck
> 
> v1:
> - https://lore.kernel.org/lkml/20220422183012.444674-4-j.neuschaefer@gmx.net/
> ---
>   drivers/watchdog/npcm_wdt.c | 18 ++++++++++++++++++
>   1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/watchdog/npcm_wdt.c b/drivers/watchdog/npcm_wdt.c
> index 28a24caa2627c..a1240a906ef2a 100644
> --- a/drivers/watchdog/npcm_wdt.c
> +++ b/drivers/watchdog/npcm_wdt.c
> @@ -3,6 +3,7 @@
>   // Copyright (c) 2018 IBM Corp.
> 
>   #include <linux/bitops.h>
> +#include <linux/clk.h>
>   #include <linux/delay.h>
>   #include <linux/interrupt.h>
>   #include <linux/kernel.h>
> @@ -43,6 +44,7 @@
>   struct npcm_wdt {
>   	struct watchdog_device  wdd;
>   	void __iomem		*reg;
> +	struct clk		*clk;
>   };
> 
>   static inline struct npcm_wdt *to_npcm_wdt(struct watchdog_device *wdd)
> @@ -66,6 +68,9 @@ static int npcm_wdt_start(struct watchdog_device *wdd)
>   	struct npcm_wdt *wdt = to_npcm_wdt(wdd);
>   	u32 val;
> 
> +	if (wdt->clk)
> +		clk_prepare_enable(wdt->clk);
> +
>   	if (wdd->timeout < 2)
>   		val = 0x800;
>   	else if (wdd->timeout < 3)
> @@ -100,6 +105,9 @@ static int npcm_wdt_stop(struct watchdog_device *wdd)
> 
>   	writel(0, wdt->reg);
> 
> +	if (wdt->clk)
> +		clk_disable_unprepare(wdt->clk);
> +
>   	return 0;
>   }
> 
> @@ -147,9 +155,15 @@ static int npcm_wdt_restart(struct watchdog_device *wdd,
>   {
>   	struct npcm_wdt *wdt = to_npcm_wdt(wdd);
> 
> +	if (wdt->clk)
> +		clk_prepare_enable(wdt->clk);
> +
>   	writel(NPCM_WTR | NPCM_WTRE | NPCM_WTE, wdt->reg);
>   	udelay(1000);
> 
> +	if (wdt->clk)
> +		clk_disable_unprepare(wdt->clk);
> +

I am trying to understand why you stop the clock here.
If the watchdog didn't reset the system by now, for whatever reason,
you explicitly don't want it to reset the system ? If so, please add
a comment describing the reason for stopping the clock here.

Thanks,
Guenter

>   	return 0;
>   }
> 
> @@ -191,6 +205,10 @@ static int npcm_wdt_probe(struct platform_device *pdev)
>   	if (IS_ERR(wdt->reg))
>   		return PTR_ERR(wdt->reg);
> 
> +	wdt->clk = devm_clk_get_optional(&pdev->dev, NULL);
> +	if (IS_ERR(wdt->clk))
> +		return PTR_ERR(wdt->clk);
> +
>   	irq = platform_get_irq(pdev, 0);
>   	if (irq < 0)
>   		return irq;
> --
> 2.35.1
>