Re: [Qemu-devel] [PATCH v2 2/3] audio: use object link instead ofqdevproperty to pass wm8750 reference

[maozy <maozhongyi@cmss.chinamobile.com>]

Hi, Philippe

On 10/13/18 2:40 AM, Philippe Mathieu-Daudé wrote:
> Hi Mao,
> 
> On 12/10/2018 14:30, Philippe Mathieu-Daudé wrote:
>> Cc'ing Eduardo and Thomas.
>>
>> On 12/10/2018 13:51, maozy wrote:
>>> Hi, Philippe
>>>
>>> On 10/12/18 5:53 PM, Philippe Mathieu-Daudé wrote:
>>>> Hi Mao,
>>>>
>>>> On 12/10/2018 10:30, Mao Zhongyi wrote:
>>>>> According to qdev-properties.h, properties of pointer type should
>>>>> be avoided, it seems a link type property is a good substitution.
>>>>>
>>>>> Cc: Jan Kiszka <jan.kiszka@web.de>
>>>>> Cc: Peter Maydell <peter.maydell@linaro.org>
>>>>> Cc: Gerd Hoffmann <kraxel@redhat.com>
>>>>> To: qemu-arm@nongnu.org
>>>>>
>>>>> Signed-off-by: Mao Zhongyi <maozhongyi@cmss.chinamobile.com>
>>>>> ---
>>>>>    hw/arm/musicpal.c          |  3 ++-
>>>>>    hw/audio/marvell_88w8618.c | 14 ++++++--------
>>>>>    2 files changed, 8 insertions(+), 9 deletions(-)
>>>>>
>>>>> diff --git a/hw/arm/musicpal.c b/hw/arm/musicpal.c
>>>>> index 3dafb41b0b..ac266f9253 100644
>>>>> --- a/hw/arm/musicpal.c
>>>>> +++ b/hw/arm/musicpal.c
>>>>> @@ -1695,7 +1695,8 @@ static void musicpal_init(MachineState *machine)
>>>>>        wm8750_dev = i2c_create_slave(i2c, TYPE_WM8750, MP_WM_ADDR);
>>>>>        dev = qdev_create(NULL, "mv88w8618_audio");
>>>>>        s = SYS_BUS_DEVICE(dev);
>>>>> -    qdev_prop_set_ptr(dev, TYPE_WM8750, wm8750_dev);
>>>>> +    object_property_set_link(OBJECT(dev), OBJECT(wm8750_dev),
>>>>> +                             TYPE_WM8750, NULL);
>>>>>        qdev_init_nofail(dev);
>>>>>        sysbus_mmio_map(s, 0, MP_AUDIO_BASE);
>>>>>        sysbus_connect_irq(s, 0, pic[MP_AUDIO_IRQ]);
>>>>> diff --git a/hw/audio/marvell_88w8618.c b/hw/audio/marvell_88w8618.c
>>>>> index cf6ce6979b..baab4a3d53 100644
>>>>> --- a/hw/audio/marvell_88w8618.c
>>>>> +++ b/hw/audio/marvell_88w8618.c
>>>>> @@ -15,6 +15,7 @@
>>>>>    #include "hw/i2c/i2c.h"
>>>>>    #include "hw/audio/wm8750.h"
>>>>>    #include "audio/audio.h"
>>>>> +#include "qapi/error.h"
>>>>>      #define MP_AUDIO_SIZE           0x00001000
>>>>>    @@ -252,6 +253,11 @@ static void mv88w8618_audio_init(Object *obj)
>>>>>        memory_region_init_io(&s->iomem, obj, &mv88w8618_audio_ops, s,
>>>>>                              "audio", MP_AUDIO_SIZE);
>>>>>        sysbus_init_mmio(dev, &s->iomem);
>>>>> +
>>>>> +    object_property_add_link(OBJECT(dev), "mv88w8618", TYPE_WM8750,
>>>>> +                             (Object **) &s->wm,
>>>>> +                             qdev_prop_allow_set_link_before_realize,
>>>>> +                             0, &error_abort);
>>>>>    }
>>>>>      static void mv88w8618_audio_realize(DeviceState *dev, Error **errp)
>>>>> @@ -279,11 +285,6 @@ static const VMStateDescription
>>>>> mv88w8618_audio_vmsd = {
>>>>>        }
>>>>>    };
>>>>>    -static Property mv88w8618_audio_properties[] = {
>>>>> -    DEFINE_PROP_PTR(TYPE_WM8750, mv88w8618_audio_state, wm),
>>>>> -    {/* end of list */},
>>>>> -};
>>>>> -
>>>>>    static void mv88w8618_audio_class_init(ObjectClass *klass, void *data)
>>>>>    {
>>>>>        DeviceClass *dc = DEVICE_CLASS(klass);
>>>>> @@ -291,9 +292,6 @@ static void
>>>>> mv88w8618_audio_class_init(ObjectClass *klass, void *data)
>>>>>        dc->realize = mv88w8618_audio_realize;
>>>>>        dc->reset = mv88w8618_audio_reset;
>>>>>        dc->vmsd = &mv88w8618_audio_vmsd;
>>>>> -    dc->props = mv88w8618_audio_properties;
>>>>> -    /* Reason: pointer property "wm8750" */
>>>>> -    dc->user_creatable = false;
>>>>
>>>> Having a link property isn't it the same restriction?
>>>
>>> This task can found in
>>> https://wiki.qemu.org/Contribute/BiteSizedTasks#Device_models
>>>
>>> Convert qdev pointer properties (defined with DEFINE_PROP_PTR) to QOM
>>> links. Example: commit 873b4d3.
>>
>> I agree with the QOM conversion (the rest of this patch), what I'm
>> wondering is if declaring this device now user_creatable is correct. I
>> don't think we can set link property from command line, but maybe I'm
>> wrong because I never investigate/tried to do it.
>>
>> Maybe devices having link property are automatically marked as
>> user_creatable = false, then your change would be correct (except you
>> should explicit that in the commit message).
>>
>> I'll post another mail on the list to ask about that.
> 
> On https://lists.gnu.org/archive/html/qemu-devel/2018-10/msg02531.html
> 
> Peter answered:
> 
>    I think whether a device with a link property is
>    user creatable might depend on what the property is
>    for and whether the device has a useful fallback for
>    "link not connected".
> 
> So if you look the realize function, there is no check on the linked object:
> 
>      static void mv88w8618_audio_realize(DeviceState *dev, Error **errp)
>      {
>          mv88w8618_audio_state *s = MV88W8618_AUDIO(dev);
> 
>          wm8750_data_req_set(s->wm, mv88w8618_audio_callback, s);
>      }
> 
> Then the called function dereference the WM8750State:
> 
>      void wm8750_data_req_set(DeviceState *dev, data_req_cb *data_req,
>                               void *opaque)
>      {
>          WM8750State *s = WM8750(dev);
> 
>          s->data_req = data_req;
>          s->opaque = opaque;
>      }
> 
> So this patch is incorrect. You should either keep the
> 'dc->user_creatable = false' line, or add a check in the realize()
> function, as here:
> 
>      static void bcm2836_realize(DeviceState *dev, Error **errp)
>      {
>          Object *obj;
>          Error *err = NULL;
> 
>          obj = object_property_get_link(OBJECT(dev), "ram", &err);
>          if (obj == NULL) {
>              error_setg(errp, "%s: required ram link not found: %s",
>                         __func__, error_get_pretty(err));
>              return;
>          }
>          ...
> 

Sorry for the delay in response, I was away for the holiday weekend.
I saw the mail you discussed and reviewed the code, I will fix it in
the next version. Thank you! I really appreciate it.

Thanks,
Mao


> Regards,
> 
> Phil.
> 
>>
>> Regards,
>>
>> Phil.
>>
>>>
>>> Thanks,
>>> Mao
>>>
>>>>
>>>>>    }
>>>>>      static const TypeInfo mv88w8618_audio_info = {
>>>>>
>>>>
>>>
>>>
>