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Date:	Sat, 22 Feb 2014 17:36:33 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Alejandro Cabrera <acabrera@...o.cujae.edu.cu>
CC:	Wim Van Sebroeck <wim@...ana.be>,
	Michal Simek <michal.simek@...inx.com>,
	linux-kernel@...r.kernel.org, monstr@...str.eu,
	linux-watchdog@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 07/11] watchdog: xilinx: Use of_property_read_u32

On 02/22/2014 07:52 PM, Alejandro Cabrera wrote:
> On 22/2/2014 3:18 PM, Guenter Roeck wrote:
>> On 02/22/2014 05:08 PM, Alejandro Cabrera wrote:
>>> On 22/2/2014 10:46 AM, Wim Van Sebroeck wrote:
>>>> Hi All,
>>>>
>>>>> Hi Michal,
>>>>>
>>>>> On Wed, Feb 12, 2014 at 02:41:21PM +0100, Michal Simek wrote:
>>>>>> Use of_property_read_u32 functions to clean probe function.
>>>>>>
>>>>>> Signed-off-by: Michal Simek<michal.simek@...inx.com>
>>>>>> Reviewed-by: Guenter Roeck<linux@...ck-us.net>
>>>>>> ---
>>>>>>
>>>>>> Changes in v3:
>>>>>> - Remove one if checking and use variable directly
>>>>>>
>>>>> Looks good.
>>>>>
>>>>> Another comment/remark.
>>>>>
>>>>>> -    pfreq = (u32 *)of_get_property(pdev->dev.of_node,
>>>>>> -                    "clock-frequency", NULL);
>>>>>> -
>>>>>> -    if (pfreq == NULL) {
>>>>>> +    rc = of_property_read_u32(pdev->dev.of_node, "clock-frequency",&pfreq);
>>>>>> +    if (rc) {
>>>>>>           dev_warn(&pdev->dev,
>>>>>>                "The watchdog clock frequency cannot be obtained\n");
>>>>>>           no_timeout = true;
>>>>>>       }
>>>>>>
>>>>>> -    tmptr = (u32 *)of_get_property(pdev->dev.of_node,
>>>>>> -                    "xlnx,wdt-interval", NULL);
>>>>>> -    if (tmptr == NULL) {
>>>>>> +    rc = of_property_read_u32(pdev->dev.of_node, "xlnx,wdt-interval",
>>>>>> + &xdev->wdt_interval);
>>>>>> +    if (rc) {
>>>>>>           dev_warn(&pdev->dev,
>>>>>>                "Parameter \"xlnx,wdt-interval\" not found\n");
>>>>>>           no_timeout = true;
>>>>>> -    } else {
>>>>>> -        xdev->wdt_interval = *tmptr;
>>>>>>       }
>>>>>>
>>>>>> -    tmptr = (u32 *)of_get_property(pdev->dev.of_node,
>>>>>> -                    "xlnx,wdt-enable-once", NULL);
>>>>>> -    if (tmptr == NULL) {
>>>>>> +    rc = of_property_read_u32(pdev->dev.of_node, "xlnx,wdt-enable-once",
>>>>>> + &enable_once);
>>>>>> +    if (rc)
>>>>>>           dev_warn(&pdev->dev,
>>>>>>                "Parameter \"xlnx,wdt-enable-once\" not found\n");
>>>>>> -        watchdog_set_nowayout(xilinx_wdt_wdd, true);
>>>>>> -    }
>>>>> All the above properties are optional. Is a warning really
>>>>> warranted in this case ? I usually associate a warning with
>>>>> something that is wrong, which is not the case here.
>>>>>
>>>>> I would encourage you to drop those warnings, but that should be
>>>>> a separate patch.
>>>> I agree with Guenter: these are not really warnings. Seperate patch is thus welcome.
>>> Hi
>>>
>>> I support Michal intention, I think it is a warning because device tree blob must have the "xlnx,wdt-enable-once" property specified in order to allow the system to be sure of the real value of this property. In addition to, this warning can be helpful to detect a wrong device tree specification.
>>>
>>
>> The dt documentation states that the properties are optional.
>>
>> Optional properties:
>> - clock-frequency       : Frequency of clock in Hz
>> - xlnx,wdt-enable-once  : 0 - Watchdog can be restarted
>>                           1 - Watchdog can be enabled just once
>> - xlnx,wdt-interval     : Watchdog timeout interval in 2^<val> clock cycles,
>> <val> is integer from 8 to 31.
>>
>> This clearly conflicts with your statement. An optional property
>> is just that, optional. If it warrants a warning, it must
>> not be optional. If you claim that not providing the properties
>> would be "wrong", why are they defined as optional ?
> Hi Guenter
>
> I didn't know that these properties was classified as optional...
> I think that they should not be, because all xilinx watchog devices (at least for microblaze processor)
> have these properties defined in theirs MPD files and theirs values can be obtained during the
> hardware specification to device tree conversion.
>> What is your definition of "wrong" and "must have" ?
> what I mean for "must have" is: if these properties can be obtained
> for all xilinx watchdog devices they must be present in the device tree because they allows
> the system (linux/user) to know exactly how a watchdog device is configured.
> Because these properties always can be obtained from hardware design there is no
> reason to leave them out from the device tree. This is why I consider that a device tree without
> these properties should be considered as "wrong" device tree.
>> How do you expect anyone to know that omitting those
>> "optional" properties is by some definition "wrong" ?
> I'm agree with you.
> Maybe these properties shouldn't be optional.
> For example suppose that "xlnx,wdt-enable-once" is missing in the device tree,
> when a watchdog daemon ask for this property what is the obtained value ?
> Independently of this value, why do not warn the user about this missing property
> when it can always be in the device tree ?
>

Really, this line of argument doesn't make any sense to me.
"xlnx,wdt-enable-once", for example, is a boolean and means
that the watchdog, when enabled, can not be stopped. It defaults
to false, and thus is inherently optional. Making it mandatory
doesn't really add any value.

Similar, the driver choses defaults for the other values.
If that is incorrect, it should not do it.

Really, something is very fishy here. Either the properties are
optional or they are not. If they are optional, the driver should
accept the fact silently. If they are mandatory, the driver should
act accordingly and bail out if the attributes are not there.

You can not have it both ways. I am close to recommending
that Wim should not accept this driver until that is sorted out.

Guenter

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