Re: Assign BAR address for pci device after hotplug

[Greg KH <greg@kroah.com>]

On Tue, Aug 02, 2016 at 09:11:09PM +0000, Chitturi, Divakar wrote:
> 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

Which pci hotplug driver?  Just the PCI Hotplug core isn't going to do
anything, you need a controller driver for your specific PCI hotplug
hardware.

> 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

How are they added/removed without a hotplug controller?

> 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. 

What architecture is this?  x86?  If so, it just uses whatever the BIOS
said was there for the last time.

> 2. Should i assign it explicitly? 

Yes.

> 3. if yes, should it be done in my driver ( in both the case i am assuming driver's probe function will be called )

No, in your pci hotplug driver, you need to handle it there.

> 4. can i use pci_assign_resource() in drivers probe function

Nope.

> 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);
> }

You need to write a pci hotplug controller driver to manage the
resources and assign them properly.  That's its responsibility, see the
PCI hotplug specification for all of the details...

good luck!

greg k-h