Re: sysbus_create_simple Vs qdev_create

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

Hi Pratik,

On 7/14/20 6:17 PM, Pratik Parvati wrote:
> Here is a brief context that might help you.
> I am referring hw/arm/versatilepb.c
> 
> The ARM PrimeCell UART (PL011) device created as follows
> 
> |dev = qdev_create(NULL, "pl011"); s = SYS_BUS_DEVICE(dev);
> qdev_prop_set_chr(dev, "chardev", chr); qdev_init_nofail(dev);
> sysbus_mmio_map(s, 0, addr); sysbus_connect_irq(s, 0, irq); |
> 
> Whereas the PL031 RTC device is created as
> 
> |/* Add PL031 Real Time Clock. */ sysbus_create_simple("pl031",
> 0x101e8000, pic[10]); |
> 
> What is the difference between these two devices creation?

Both devices inherit SysBusDevice, which itself inherits QDev.

You can create QDev objects with the qdev API, and
SysBusDevice objects with the sysbus API.

sysbus_create_simple() is a condensed helper, but only allow you
to pass qemu_irq objects, not a 'chardev' property. So for this
case you have to use the qdev API instead.

> How do I know
> which method to use while creating an object?

SysBusDevice are plugged onto a bus. QDev aren't.
The sysbus API results in smaller code, easier to review.

> 
> Thanks & Regards,
> 
> Pratik
> 
> 
> On Tue, Jul 14, 2020 at 9:39 PM Pratik Parvati <pratikp@vayavyalabs.com
> <mailto:pratikp@vayavyalabs.com>> wrote:
> 
>     Hi Support team,
> 
>     Can someone please guide me to understand the difference between
>     *sysbus_create_simple *and *qdev_create*?.
> 
>     I understand that these two methods are used to create a new device.
>     But, when to use these functions is not clear to me.
> 
>     Regards,
>     Pratik
>