Peter Maydell <peter.mayd...@linaro.org> writes:
> On 12 July 2017 at 12:22, Markus Armbruster <arm...@redhat.com> wrote:
>> Peter Maydell <peter.mayd...@linaro.org> writes:
>>
>>> In some situations it's useful to have a qdev property which doesn't
>>> automatically set its default value when qdev_property_add_static is
>>> called (for instance when the default value is not constant).
>>>
>>> Support this by adding a flag to the Property struct indicating
>>> whether to set the default value. This replaces the existing test
>>> for whether the PorpertyInfo set_default_value function pointer is
>>
>> PropertyInfo
>>
>>> NULL, and we set the .set_default field to true for all those cases
>>> of struct Property which use a PropertyInfo with a non-NULL
>>> set_default_value, so behaviour remains the same as before.
>>>
>>> We define two new macros DEFINE_PROP_SIGNED_NODEFAULT and
>>> DEFINE_PROP_UNSIGNED_NODEFAULT, to cover the most plausible use cases
>>> of wanting to set an integer property with no default value.
>>
>> Your text makes me wonder what is supposed to set the default value
>> then. Glancing ahead to PATCH 3, it looks like method instance_init()
>> is. Can you think of a scenario where something else sets it?
>
> OK, proposed extra paragraph for commit message:
>
> This gives us the semantics of:
> * if .set_default is true and .info->set_default_value is not NULL,
> then .defval is used as the the default value of the property
If I read your patch correctly, then this should be "if .set_default is
true, then .info->set_default_value() must not be null, and .defval is
used ..."
> * otherwise, the property system does not set any default, and
> the field will retain whatever initial value it was given by
> the device's .instance_init method
>
> (to go just before the "We define two new macros..." para.)
>
>>> --- a/include/hw/qdev-core.h
>>> +++ b/include/hw/qdev-core.h
>>> @@ -226,6 +226,7 @@ struct Property {
>>> PropertyInfo *info;
>>> ptrdiff_t offset;
>>> uint8_t bitnr;
>>> + bool set_default;
>>
>> Your chance to add the very first comment to struct Property (its
>> existing undocumentedness is an embarrassment, but not this patch's
>> problem). Let's write down that this flag governs where (integer)
>> default values come from, either from member devfal or from method
>> instance_init() or whatever.
>
> OK, how about
> /**
> * Property:
> * @set_default: true if the default value should be set from @defval
> * (if false then no default value is set by the property system
> * and the field retains whatever value it was given by instance_init).
> * @defval: default value for the property. This is used only if @set_default
> * is true and @info->set_default_value is not NULL.
> */
Again, I believe ->set_default_value() must not be null when
->set_default is true.
>
> ?
>
> thanks
> -- PMM
