linux-kernel - Re: [RFC PATCH v2] watchdog: sp805: Add clock-frequency property

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Date:   Mon, 9 Jul 2018 06:45:09 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Srinath Mannam <srinath.mannam@...adcom.com>,
        wim@...ux-watchdog.org
Cc:     ray.jui@...adcom.com, vladimir.olovyannikov@...adcom.com,
        vikram.prakash@...adcom.com, scott.branden@...adcom.com,
        sudeep.holla@....com, linux-watchdog@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2] watchdog: sp805: Add clock-frequency property

On 07/09/2018 03:19 AM, Srinath Mannam wrote:
> When using ACPI node, binding clock devices are
> not available as device tree, So clock-frequency
> property given in _DSD object of ACPI device is
> used to calculate Watchdog rate.
> 
> Signed-off-by: Srinath Mannam <srinath.mannam@...adcom.com>
> ---
>   drivers/watchdog/sp805_wdt.c | 34 ++++++++++++++++++++++++++--------
>   1 file changed, 26 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/watchdog/sp805_wdt.c b/drivers/watchdog/sp805_wdt.c
> index 9849db0..ad5ed64 100644
> --- a/drivers/watchdog/sp805_wdt.c
> +++ b/drivers/watchdog/sp805_wdt.c
> @@ -11,6 +11,7 @@
>    * warranty of any kind, whether express or implied.
>    */
>   
> +#include <linux/acpi.h>
>   #include <linux/device.h>
>   #include <linux/resource.h>
>   #include <linux/amba/bus.h>
> @@ -22,6 +23,7 @@
>   #include <linux/math64.h>
>   #include <linux/module.h>
>   #include <linux/moduleparam.h>
> +#include <linux/of.h>
>   #include <linux/pm.h>
>   #include <linux/slab.h>
>   #include <linux/spinlock.h>
> @@ -65,6 +67,7 @@ struct sp805_wdt {
>   	spinlock_t			lock;
>   	void __iomem			*base;
>   	struct clk			*clk;
> +	u64				rate;
>   	struct amba_device		*adev;
>   	unsigned int			load_val;
>   };
> @@ -80,7 +83,7 @@ static int wdt_setload(struct watchdog_device *wdd, unsigned int timeout)
>   	struct sp805_wdt *wdt = watchdog_get_drvdata(wdd);
>   	u64 load, rate;
>   
> -	rate = clk_get_rate(wdt->clk);
> +	rate = wdt->rate;
>   
>   	/*
>   	 * sp805 runs counter with given value twice, after the end of first
> @@ -106,9 +109,7 @@ static int wdt_setload(struct watchdog_device *wdd, unsigned int timeout)
>   static unsigned int wdt_timeleft(struct watchdog_device *wdd)
>   {
>   	struct sp805_wdt *wdt = watchdog_get_drvdata(wdd);
> -	u64 load, rate;
> -
> -	rate = clk_get_rate(wdt->clk);
> +	u64 load;
>   
>   	spin_lock(&wdt->lock);
>   	load = readl_relaxed(wdt->base + WDTVALUE);
> @@ -118,7 +119,7 @@ static unsigned int wdt_timeleft(struct watchdog_device *wdd)
>   		load += wdt->load_val + 1;
>   	spin_unlock(&wdt->lock);
>   
> -	return div_u64(load, rate);
> +	return div_u64(load, wdt->rate);
>   }
>   
>   static int
> @@ -228,10 +229,27 @@ sp805_wdt_probe(struct amba_device *adev, const struct amba_id *id)
>   	if (IS_ERR(wdt->base))
>   		return PTR_ERR(wdt->base);
>   
> -	wdt->clk = devm_clk_get(&adev->dev, NULL);
> -	if (IS_ERR(wdt->clk)) {
> +	if (adev->dev.of_node) {
> +		wdt->clk = devm_clk_get(&adev->dev, NULL);
> +		if (IS_ERR(wdt->clk)) {
> +			ret = PTR_ERR(wdt->clk);
> +			wdt->clk = NULL;

Clearing wdt->clk is useless.

> +		} else
> +			wdt->rate = clk_get_rate(wdt->clk);

The else branch should be in { } as well per coding style.

> +	} else if (has_acpi_companion(&adev->dev)) {
> +		/*
> +		 * When Driver probe with ACPI device, clock devices
> +		 * are not available, so watchdog rate get from
> +		 * clock-frequency property given in _DSD object.
> +		 */
> +		device_property_read_u64(&adev->dev, "clock-frequency",
> +				&wdt->rate);

Continuation line alignment is off.

Still not documented. Maybe that is common for ACPI devices nowadays.
If so, I'll need at least a pointer to a document or something declaring
that ACPI devices do not use well documented properties, and a confirmation
that using such properties is acceptable in the Linux kernel.

> +		if (!wdt->rate)
> +			ret = -ENODEV;
> +	}
> +
> +	if (ret) {
>   		dev_warn(&adev->dev, "Clock not found\n");
> -		ret = PTR_ERR(wdt->clk);
>   		goto err;
>   	}

Please move the error handling to where the error occurs. While doing that,
please change the message to dev_err() - this is an error, not a warning -
and change the second error message to match the error (it did not find
the property).

Also, return directly - the goto just generates another error message
which is ridiculous.

Thanks,
Guenter