Assign BAR address for pci device after hotplug

Hi

Below are two scenarios for which i would like to understand the right way to assign the BAR address for my PCI device

Device details:
pci switch upstrem port connected to root complex
pci switch downstream port 1 connected to my_pci_device
my_pci_device is FPGA
FPGA has bunch of controllers and other logic

Driver details:
Have a dedicated pci kernel driver for my_device
Enabled pcihp kernel driver
 
At power on, BIOS assigns/reserves specific region of memory for my pci device.
during the linux boot process, pci core will assign the bar and other initialization and call my
probe function in the driver. probe function will perform some initialization which includes reading
the BAR and setting some registers in IO space of the device. 

Scn1:
At some point the device is removed and reinserted

Scn2:
At some point similar device is inserted in a new pci slot

In both the scenarios explained about, BIOS is not involved as system was never turned off completely. So
1. how do we obtain the BAR address for the device. 
2. Should i assign it explicitly? 
3. if yes, should it be done in my driver ( in both the case i am assuming driver's probe function will be called )
4. can i use pci_assign_resource() in drivers probe function
5. is something like below the right way to do it ?

static int my_probe(struct pci_dev *pdev, const struct pci_device_id *id)
{
         if( pci_resource_start (pdev,BAR0) <= 0) {
                pr_debug(" Assign BAR0 \n");
	ret = pci_assign_resource(pdev,BAR0);
                if( 0 > ret) {
                    dev_err(&pdev->dev, " Failed to assign resource \n");
                    return ret;
                }
        }
		
       ret = pci_enable_device(pdev);
       ret = pci_request_regions(pdev, dev_driver_string(&pdev->dev));
       base_addr = pci_iomap(pdev, BAR0, 0);
}

Thanks
Divakar