Re: [PATCH v6 5/9] qdev-clock: introduce an init array to ease the device construction

[Damien Hedde]

On 12/2/19 4:13 PM, Peter Maydell wrote:
> On Wed, 4 Sep 2019 at 13:56, Damien Hedde <address@hidden> wrote:
>>
>> Introduce a function and macro helpers to setup several clocks
>> in a device from a static array description.
>>
>> An element of the array describes the clock (name and direction) as
>> well as the related callback and an optional offset to store the
>> created object pointer in the device state structure.
>>
>> The array must be terminated by a special element QDEV_CLOCK_END.
>>
>> This is based on the original work of Frederic Konrad.
>>
>> Signed-off-by: Damien Hedde <address@hidden>
>> Reviewed-by: Philippe Mathieu-Daudé <address@hidden>
>> ---
>>  hw/core/qdev-clock.c    | 26 ++++++++++++++++
>>  include/hw/qdev-clock.h | 67 +++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 93 insertions(+)
>>
>> diff --git a/hw/core/qdev-clock.c b/hw/core/qdev-clock.c
>> index bebdd8fa15..32ad45c061 100644
>> --- a/hw/core/qdev-clock.c
>> +++ b/hw/core/qdev-clock.c
>> @@ -153,3 +153,29 @@ void qdev_connect_clock_out(DeviceState *dev, const 
>> char *name, ClockIn *clk,
>>
>>      clock_connect(clk, clkout);
>>  }
>> +
>> +void qdev_init_clocks(DeviceState *dev, const ClockPortInitArray clocks)
>> +{
>> +    const struct ClockPortInitElem *elem;
>> +
>> +    assert(dev);
>> +    assert(clocks);
> 
> More unnecessary asserts, I think.
> 
> 
> 
>> +/**
>> + * ClockInitElem:
>> + * @name: name of the clock (can't be NULL)
>> + * @is_output: indicates whether the clock is input or output
>> + * @callback: for inputs, optional callback to be called on clock's update
>> + * with device as opaque
>> + * @offset: optional offset to store the ClockIn or ClockOut pointer in 
>> device
>> + * state structure (0 means unused)
>> + */
>> +struct ClockPortInitElem {
>> +    const char *name;
>> +    bool is_output;
>> +    ClockCallback *callback;
>> +    size_t offset;
>> +};
>> +
>> +#define clock_offset_value(_type, _devstate, _field) \
>> +    (offsetof(_devstate, _field) + \
>> +     type_check(_type *, typeof_field(_devstate, _field)))
> 
> Avoid leading underscores, please.
> 
>> +
>> +#define QDEV_CLOCK(_is_output, _type, _devstate, _field, _callback) { \
>> +    .name = (stringify(_field)), \
>> +    .is_output = _is_output, \
>> +    .callback = _callback, \
>> +    .offset = clock_offset_value(_type, _devstate, _field), \
>> +}
>> +
>> +/**
>> + * QDEV_CLOCK_(IN|OUT):
>> + * @_devstate: structure type. @dev argument of qdev_init_clocks below must 
>> be
>> + * a pointer to that same type.
> 
> It's a bit unclear what "below" here is referring to. Maybe
> just have this be "@devstate: name of a C struct type"
> and then explain below...
> 
>> + * @_field: a field in @_devstate (must be ClockIn* or ClockOut*)
>> + * @_callback: (for input only) callback (or NULL) to be called with the 
>> device
>> + * state as argument
>> + *
> 
> ...here, where we can have a paragraph giving the purpose
> of the macro:
> 
> "Define an entry in a ClockPortInitArray which is intended
> to be passed to qdev_init_clocks(), which should be called
> with an @dev argument which is a pointer to the @devstate
> struct type."

Sounds good.

> 
>> + * The name of the clock will be derived from @_field
> 
> Derived how? Guessing from the stringify(_field) above that it
> will be the same as the field name ?

yes.

> 
> It makes sense to hardcode the opaque pointer for the callback to be
> the device pointer.
> 
> 
>> + */
>> +#define QDEV_CLOCK_IN(_devstate, _field, _callback) \
>> +    QDEV_CLOCK(false, ClockIn, _devstate, _field, _callback)
>> +
>> +#define QDEV_CLOCK_OUT(_devstate, _field) \
>> +    QDEV_CLOCK(true, ClockOut, _devstate, _field, NULL)
>> +
>> +/**
>> + * QDEV_CLOCK_IN_NOFIELD:
>> + * @_name: name of the clock
>> + * @_callback: callback (or NULL) to be called with the device state as 
>> argument
>> + */
>> +#define QDEV_CLOCK_IN_NOFIELD(_name, _callback) { \
>> +    .name = _name, \
>> +    .is_output = false, \
>> +    .callback = _callback, \
>> +    .offset = 0, \
>> +}
> 
> When would we want to use this one ?

If the callback interaction is enough, we don't need to access the clock
object directly. So we don't need the field in the device state
structure. I can remove this macro for sake of simplicity.

--
Damien