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From:   Srinath Mannam <srinath.mannam@broadcom.com>
Date:   Tue, 10 Jul 2018 13:27:55 +0530
Message-ID: <CABe79T4qj6SaZJzTn_ZY7XfGkj_z6JJ57+WfMm3zGE7XLbT4Lg@mail.gmail.com>
Subject: Re: [RFC PATCH v2] watchdog: sp805: Add clock-frequency property
To:     Guenter Roeck <linux@roeck-us.net>
Cc:     wim@linux-watchdog.org, Ray Jui <ray.jui@broadcom.com>,
        Vladimir Olovyannikov <vladimir.olovyannikov@broadcom.com>,
        Vikram Prakash <vikram.prakash@broadcom.com>,
        Scott Branden <scott.branden@broadcom.com>,
        Sudeep Holla <sudeep.holla@arm.com>,
        linux-watchdog@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Hi Guenter,

Thank you for your feedback. Please find my answers in lined.

On Mon, Jul 9, 2018 at 7:15 PM, Guenter Roeck <linux@roeck-us.net> wrote:
> 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@broadcom.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.

If not, clk_prepare_enable and clk_disable_unprepare functions calls
made in this driver will crash.

>
>> +               } else
>> +                       wdt->rate = clk_get_rate(wdt->clk);
>
>
> The else branch should be in { } as well per coding style.
I will add the change.
>
>> +       } 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.
I missed it, Thank you, I will make the change.
>
> 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.
>
patches listed below has same approach to add ACPI support.
ex:
1. commit 515da746983bc6382e380ba8b1ce9345a9550ffe
Author: Naveen Kaje <nkaje@codeaurora.org>
Date:   Tue Oct 11 10:27:56 2016 -0600

    i2c: qup: add ACPI support

2. commit 82a19035d000c8b4fd7d6f61b614f63dec75d389
Author: Lendacky, Thomas <Thomas.Lendacky@amd.com>
Date:   Fri Jan 16 12:47:16 2015 -0600

    amd-xgbe: Add ACPI support

>> +               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.
Thank you, I will add the changes.
>
> Thanks,
> Guenter

Regards,
Srinath.